Polyethylene v. Polypropylene

[Moondog]

Those are indeed impressive numbers Gary, I guess what I would ask you is what do you store your personal collection in?

 

Not trying to be my normal overly smart alec self, just honestly curious.

 

Poly, or Mylar? Because my preference comes down to more aesthetics rather then preservation qualities even though I feel Mylar superior to poly hands down.

 

Ze-

 

 

Ah, you again get to the heart of the matter, Kenny. It must be due to your astute and keen knowledge of the collector mentality.

 

Which plastic one uses for their collection is a matter of aesthetics. If you don't like the filmy clarity of PE and prefer the glassy clarity of PP - no problem. Each will do a fine job of protecting your collection from storage damage and minor handling. Mylites do exactly the same thing.

 

If you're going to be showing off your books or you plan to sell some more expensive items, then you need more protection against handling. That's where 4-mil Mylar does the best job. It's perfect for display and protects against handling damage.

 

Someone on this thread mentioned that the comics turn the PE bags yellow, yet the books stay white inside. This isn't correct. The bags turn yellow due to the environment and the passage of time. Nothing happens regarding the book and the bag. If the books are white inside it's because the environment has been cool, dark and dry.

 

Personally I use all 3 plastics. I have my dealer box stock in PP (for the most part) because the superior clarity helps make the book look better. I have my best dealer stock in 4-mil Mylar.

 

Regarding my collection, I have low-value items in PE. My ashcans are, of course, in 4-mil Mylar as are other valuable books.

 

 

 

 

 

 

[divad]

what do you guys use generally -- obviously I use mylite2s and full backs for the expensive stuff... but just the generic books... what is everyone's preference?

 

I don't own any "generic" books . . .

 

 

[divad]

Re: Polyethylene v. Polypropylene

 

They both work equally well for picking up the kitty poo . . .

[shadroch]

Its my understanding that the PP bags are superior.Perhaps I am brainwashed,but thats my understanding.

It doesn't matter to me as any book I deem a keeper goes in at least a myliteplus,and the rest go into whatever I have laying around. I can't remember the last time I bought any sort of polywhatever bag.

 

Same here. I have tons of books still in both PE and PP that have been in them for at least 15 years and the books haven't been affected by the bags. The PP bags are overall better looking and seemed to have held up better than the PE bags (some of which are sticky...nothing to do with the Leather and Lace and Black Kiss comics contained within).

 

 

Before I sold my business to Diamond, I sold over 800 million plastic bags under the ComiCovers brand. Of the 800 million, 500 million were PE, the remainder PP. I've said this countless times over the years to collectors, retailers and archivists:

 

PE is no better than PP. PP is no better than PE. They are different plastics but they perform the same service. Polyester film (Mylar) is basically the same - but is superior to PP and PE because it's thicker (except if it's a Mylite - then it's really no better - sorry, Kenny!).

 

It's important to know that bags made of these materials do not protecting your paper collectibles from aging.

REPEAT: None of these bags are protecting your comic books from aging.

 

They are simply a means of protecting your comics from storage and handling damage. Storage and handling damage = bugs, rodents, water, handling, etc.

 

A cool, dark and dry environment will person_having_a_hard_time_understanding_my_point the aging process.

 

 

 

As I remember it,you switched from the PE bags to PP bags,no?You started out selling the PE bags but then switched over to mostly if not totally PP bags,so that saying you sold 500Million ofone and 300 million of the other isn't any sort of testament of which type sold better,just that you sold PE bags for a longer period of time.Not that I'm implying that you did,just trying to clarify something.

 

800 million comic bags sold? Damn,that is scary.And you've been out of the biz for quite awhile now.

 

[Moondog]

Its my understanding that the PP bags are superior.Perhaps I am brainwashed,but thats my understanding.

It doesn't matter to me as any book I deem a keeper goes in at least a myliteplus,and the rest go into whatever I have laying around. I can't remember the last time I bought any sort of polywhatever bag.

 

Same here. I have tons of books still in both PE and PP that have been in them for at least 15 years and the books haven't been affected by the bags. The PP bags are overall better looking and seemed to have held up better than the PE bags (some of which are sticky...nothing to do with the Leather and Lace and Black Kiss comics contained within).

 

 

Before I sold my business to Diamond, I sold over 800 million plastic bags under the ComiCovers brand. Of the 800 million, 500 million were PE, the remainder PP. I've said this countless times over the years to collectors, retailers and archivists:

 

PE is no better than PP. PP is no better than PE. They are different plastics but they perform the same service. Polyester film (Mylar) is basically the same - but is superior to PP and PE because it's thicker (except if it's a Mylite - then it's really no better - sorry, Kenny!).

 

It's important to know that bags made of these materials do not protecting your paper collectibles from aging.

REPEAT: None of these bags are protecting your comic books from aging.

 

They are simply a means of protecting your comics from storage and handling damage. Storage and handling damage = bugs, rodents, water, handling, etc.

 

A cool, dark and dry environment will person_having_a_hard_time_understanding_my_point the aging process.

 

 

 

As I remember it,you switched from the PE bags to PP bags,no?You started out selling the PE bags but then switched over to mostly if not totally PP bags,so that saying you sold 500Million ofone and 300 million of the other isn't any sort of testament of which type sold better,just that you sold PE bags for a longer period of time.Not that I'm implying that you did,just trying to clarify something.

 

800 million comic bags sold? Damn,that is scary.And you've been out of the biz for quite awhile now.

 

 

Your recollection is close. I added PP in the late '80s due to it's much cheaper (at the time) price. I then carried both, but PP was the most popular, especially with speculators) due to its superior clarity.

[Moondog]

Shad:

 

Your recollection is close. I added PP in the late '80s due to it's much cheaper (at the time) price. I then carried both, but PP was the most popular (especially with speculators) due to its superior clarity. From '89 to '93 I sold over 100 million bags each year. It was amazing. I supplied both Diamond and Capital City. At one time ComiCovers were sold in every state in the Union.

[shadroch]

Gary,

Do you have any idea what percentage of the market you had? I think you were the market leader,but were you the majority supplier but Its scary to think that 100 million plus comics from that time were preserved each year.I wonder how those numbers compare to supplies sold today..

[ShoNuff-migration]

PE is no better than PP. PP is no better than PE. They are different plastics but they perform the same service. Polyester film (Mylar) is basically the same - but is superior to PP and PE because it's thicker (except if it's a Mylite - then it's really no better - sorry, Kenny!).

Are you trying to say that the only difference between Polyethylene/Polypropylene and Mylar is the thickness? And that using the thinner mylar (mylites) is no better than using either PE or PE?

 

If so...sorry...but I'm not buying it.

[Moondog]

PE is no better than PP. PP is no better than PE. They are different plastics but they perform the same service. Polyester film (Mylar) is basically the same - but is superior to PP and PE because it's thicker (except if it's a Mylite - then it's really no better - sorry, Kenny!).

Are you trying to say that the only difference between Polyethylene/Polypropylene and Mylar is the thickness? And that using the thinner mylar (mylites) is no better than using either PE or PE?

 

If so...sorry...but I'm not buying it.

 

That's exactly what I'm saying. If you're trying to person_having_a_hard_time_understanding_my_point the aging process, you need the right environment (cool, dark and dry). The bag will have nothing to do with it.

 

Mylites (polyester film) will not breakdown as quickly as PE or PP and retain their clarity longer, but they don't protect the comic book inside any better than PE or PP against storage and handling damage.

 

If you don't believe me, just ask the Library of Congress. They use polyester film (thick film - not Mylites) to protect their most treasured documents because it's clearer, thicker and stiffer than the other plastics - it's perfect for what they're main goal is - preserve, but make available important paper items.. But the environment that the documents are stored in is overwhelmingly the most important factor.

 

Mylites. Now that's good marketing. (thumbs u

 

That being said, I store my most important books in 4-mil Mylar. I don't use Mylites because they're just too expensive for the purpose they're used for (protecting inexpensive books). I prefer PE but also use PP.

 

I would never use Mylites on important, expensive books. They just don't protect well enough.

 

 

 

 

 

 

[Moondog]

Gary,

Do you have any idea what percentage of the market you had? I think you were the market leader,but were you the majority supplier but Its scary to think that 100 million plus comics from that time were preserved each year.I wonder how those numbers compare to supplies sold today..

 

Well, since DCD and CCD together controlled about 75% of the new comics market during this period of time I believe I had close to 75% of the market. We could determine this more definitely by looking up the total volume of comics sold during these years.

 

When the market imploded in '94 so did my volume. In '94 it shrank to 50 million. '95 was 20 million. It was remarkable. It's important to note that CCD had dropped ComiCovers in '94 and started importing bags from China and Brazil during this time.

[ShoNuff-migration]

PE is no better than PP. PP is no better than PE. They are different plastics but they perform the same service. Polyester film (Mylar) is basically the same - but is superior to PP and PE because it's thicker (except if it's a Mylite - then it's really no better - sorry, Kenny!).

Are you trying to say that the only difference between Polyethylene/Polypropylene and Mylar is the thickness? And that using the thinner mylar (mylites) is no better than using either PE or PE?

 

If so...sorry...but I'm not buying it.

 

That's exactly what I'm saying. If you're trying to person_having_a_hard_time_understanding_my_point the aging process, you need the right environment (cool, dark and dry). The bag will have nothing to do with it.

 

Mylites (polyester film) will not breakdown as quickly as PE or PP and retain their clarity longer, but they don't protect the comic book inside any better than PE or PP against storage and handling damage.

 

If you don't believe me, just ask the Library of Congress. They use polyester film (thick film - not Mylites) to protect their most treasured documents because it's clearer, thicker and stiffer than the other plastics - it's perfect for what they're main goal is - preserve, but make available important paper items.. But the environment that the documents are stored in is overwhelmingly the most important factor.

 

Mylites. Now that's good marketing. (thumbs u

 

That being said, I store my most important books in 4-mil Mylar. I don't use Mylites because they're just too expensive for the purpose they're used for (protecting inexpensive books). I prefer PE but also use PP.

 

I would never use Mylites on important, expensive books. They just don't protect well enough.

You mentioned that polyester film (Mylars/Mylites) will not break down as quickly as PE or PP. When material breaks down, it releases contaminants.

 

You also said that if you're trying to person_having_a_hard_time_understanding_my_point the aging process, you need the right environment (cool, dark and dry)...and that the bag will have nothing to do with it. I disagree here (in part) as well. While you do need cool, dark and dry storage conditions, if the bag used for storage breaks down, it will also have an effect on the aging process. Any cheap plastic with a thick backing board is capable of offering protection against handling damage, but that doesn't mean I'd want to store my comics in it, even if it was free and the books were being stored in optimal storage conditions.

 

The purpose of the backing board is to offer rigidity and protection against handling damage...while the bag is designed to hold the book and board in place while offering protection against outside contaminants such as dust, moisture, fingerprints, etc. So with regards to which bag is the safest for long-term storage of paper collectables without passively contributing to the degredation of it, polyester film is superior, regardless of its thickness.

[selegue]

Hows this....

 

 

Why polyethylene rather than polyproylene?

 

 

--------------------------------------------------------------------------------

 

 

AussieRuss, I hope you didn't write this article because it is a crock of nonsense. Its accuracy is every bit as careful as its proofreading.

 

I hardly know where to start. Let's just concentrate on a few paragraphs.

 

 

In more chemistry-speak, propylene (CH3CH:CH2) is is a sub-stratum of ethylene. Ethylene is the purest form of the base chemical and thus the purer better of the two. Consider this example: Suppose you were looking for the perfect gene to clone a tough guy. Now, would you rather have the genes from the son of a tough guy or fom the original tough guy, in this case, the son's father? Obviously, you want the purest tough guy genes, so you would go with the father. Polyethylene is like the father; polypropylene is like the son. See definitions below.

 

Propene (propylene) used to make polypropylene is every bit as pure as ethene (ethylene) used to make polyethylene. If the monomers are not pure, the catalysts have a very short lifetime. Propene being a "sub-stratum" (What??) of ethene has nothing to do with purity. Genes from the son of a tough guy. (What???)

 

 

Due to its rigitity, polypropylene sleeves are more prone to tear, especially at the seams. Try this experiment if you don't believe this. Take an ordinary piece of writing paper (rigid) and a common paper towel (pliable). Try to gently tear each one. The paper tears readily, while you have to give the towel a little more of a tug to tear it. It actually kind of resists tearing by having some flexibility. The same principle applies for propylene vs. ethylene. The ethylene base provides more "give" and thus stronger seams and less likelyhood of tearing.

 

 

Does anyone here really think that it's easier to rip a sheet of writing paper compared to a paper towel, or that the analogy has anything to do with polyethylene vs. polypropylene?

 

 

Polyethylene costs more. Simple logic dictates that it should be a superior product and it is. It costs more because it is a product of higher purity (100% Virgin) in addition to the advantages already presented, and will outlast and outperform any derivative product. Polyethylene provides better protection for both the short and long term.

 

"Product of higher purity?" Higher cost is a guarantee of higher performance?

 

One reason that mylar (PET, polyethylene terephthalate) provides better archival protection for paper goods is that its oxygen permeability is much lower than PE or PP, down in in the 1% range (hard to find an exact number without knowing the exact specs of the material in use).

 

The wikipedia articles on polyethylene, polypropylene and PET (mylar) are pretty good. Those would be a much better starting point than this claptrap. Notice that there are many different kinds of PE and PP -- the chain length and exact properties depend on the manufacturing process.

 

Jack

[shiverbones]

the wealth of information from experts in their field on these boards is tremendous. Thanks for the rebuttle Jack, I was really wondering about that myself.

[shadroch]

It's important to note that CCD had dropped ComiCovers in '94 and started importing bags from China and Brazil during this time.

 

 

 

Where were your bags made?

[Moondog]

It's important to note that CCD had dropped ComiCovers in '94 and started importing bags from China and Brazil during this time.

 

 

 

Where were your bags made?

 

Our PP was manufactured in New Jersey and our PE here in Chicago.

 

American made - all the way!

[Moondog]

PE is no better than PP. PP is no better than PE. They are different plastics but they perform the same service. Polyester film (Mylar) is basically the same - but is superior to PP and PE because it's thicker (except if it's a Mylite - then it's really no better - sorry, Kenny!).

Are you trying to say that the only difference between Polyethylene/Polypropylene and Mylar is the thickness? And that using the thinner mylar (mylites) is no better than using either PE or PE?

 

If so...sorry...but I'm not buying it.

 

That's exactly what I'm saying. If you're trying to person_having_a_hard_time_understanding_my_point the aging process, you need the right environment (cool, dark and dry). The bag will have nothing to do with it.

 

Mylites (polyester film) will not breakdown as quickly as PE or PP and retain their clarity longer, but they don't protect the comic book inside any better than PE or PP against storage and handling damage.

 

If you don't believe me, just ask the Library of Congress. They use polyester film (thick film - not Mylites) to protect their most treasured documents because it's clearer, thicker and stiffer than the other plastics - it's perfect for what they're main goal is - preserve, but make available important paper items.. But the environment that the documents are stored in is overwhelmingly the most important factor.

 

Mylites. Now that's good marketing. (thumbs u

 

That being said, I store my most important books in 4-mil Mylar. I don't use Mylites because they're just too expensive for the purpose they're used for (protecting inexpensive books). I prefer PE but also use PP.

 

I would never use Mylites on important, expensive books. They just don't protect well enough.

You mentioned that polyester film (Mylars/Mylites) will not break down as quickly as PE or PP. When material breaks down, it releases contaminants.

 

You also said that if you're trying to person_having_a_hard_time_understanding_my_point the aging process, you need the right environment (cool, dark and dry)...and that the bag will have nothing to do with it. I disagree here (in part) as well. While you do need cool, dark and dry storage conditions, if the bag used for storage breaks down, it will also have an effect on the aging process. Any cheap plastic with a thick backing board is capable of offering protection against handling damage, but that doesn't mean I'd want to store my comics in it, even if it was free and the books were being stored in optimal storage conditions.

 

The purpose of the backing board is to offer rigidity and protection against handling damage...while the bag is designed to hold the book and board in place while offering protection against outside contaminants such as dust, moisture, fingerprints, etc. So with regards to which bag is the safest for long-term storage of paper collectables without passively contributing to the degredation of it, polyester film is superior, regardless of its thickness.

 

Shonuf:

 

When I say that PE and PP "breakdown" faster, I'm referring to the PE turning filmy and yellowing and PP getting stretchy and wavy.

 

You can believe what you want regarding Mylar. As I said, I use 4-mil Mylar because it protects better than 2-mil PP, 3-mil PE or 1 or 2 mil Mylites. I've been in this hobby for nearly 50 years and started retailing in 1975. I've run across hundreds of thousands of comic books in every type of plastic bag imaginable. In all this time and all those comics I've never once seen a case where the bag caused any harm to the comic book inside. Even the yellowest, dirtiest, stickiest Baggie from the mid-60's had pristine books inside.

 

Just look at the threads that have popped up here lately for the nearly 30-year-old Gold Keys that are still "3 in a bag". Those comics are as glossy and beautiful as the day they were printed. The bags look like s h i t, but the comics are pristine.

 

I realized that I have some cheap books in my collection that have been stored in PE for nearly 25 years. I just checked them and the comics and bags are just fine (good storage environment obviously).

 

The evidence is overwhelming.

 

Bill Cole's marketing (along with Ernie Gerber's and yours truly) helped persuade collectors that they needed better protection for their comics than they could get using household products (Baggies, Saran Wrap). Bill and Ernie said that "cheap plastics" could cause harm to your books, and in the past 30 years millions of dollars have been spent trying to convince collectors that they needed more protection than they could get using cheap alternatives.

 

That being said, collectors (including myself) are proud of our books and want them to look as good as possible. Mylar, both 4-mil and Mylites, do make our books look pretty and that's probably the overwhelming reason these products are used.

 

 

 

[Moondog]

Hows this....

 

 

Why polyethylene rather than polyproylene?

 

 

--------------------------------------------------------------------------------

 

 

AussieRuss, I hope you didn't write this article because it is a crock of nonsense. Its accuracy is every bit as careful as its proofreading.

 

I hardly know where to start. Let's just concentrate on a few paragraphs.

 

 

In more chemistry-speak, propylene (CH3CH:CH2) is is a sub-stratum of ethylene. Ethylene is the purest form of the base chemical and thus the purer better of the two. Consider this example: Suppose you were looking for the perfect gene to clone a tough guy. Now, would you rather have the genes from the son of a tough guy or fom the original tough guy, in this case, the son's father? Obviously, you want the purest tough guy genes, so you would go with the father. Polyethylene is like the father; polypropylene is like the son. See definitions below.

 

Propene (propylene) used to make polypropylene is every bit as pure as ethene (ethylene) used to make polyethylene. If the monomers are not pure, the catalysts have a very short lifetime. Propene being a "sub-stratum" (What??) of ethene has nothing to do with purity. Genes from the son of a tough guy. (What???)

 

 

Due to its rigitity, polypropylene sleeves are more prone to tear, especially at the seams. Try this experiment if you don't believe this. Take an ordinary piece of writing paper (rigid) and a common paper towel (pliable). Try to gently tear each one. The paper tears readily, while you have to give the towel a little more of a tug to tear it. It actually kind of resists tearing by having some flexibility. The same principle applies for propylene vs. ethylene. The ethylene base provides more "give" and thus stronger seams and less likelyhood of tearing.

 

 

Does anyone here really think that it's easier to rip a sheet of writing paper compared to a paper towel, or that the analogy has anything to do with polyethylene vs. polypropylene?

 

 

Polyethylene costs more. Simple logic dictates that it should be a superior product and it is. It costs more because it is a product of higher purity (100% Virgin) in addition to the advantages already presented, and will outlast and outperform any derivative product. Polyethylene provides better protection for both the short and long term.

 

"Product of higher purity?" Higher cost is a guarantee of higher performance?

 

One reason that mylar (PET, polyethylene terephthalate) provides better archival protection for paper goods is that its oxygen permeability is much lower than PE or PP, down in in the 1% range (hard to find an exact number without knowing the exact specs of the material in use).

 

The wikipedia articles on polyethylene, polypropylene and PET (mylar) are pretty good. Those would be a much better starting point than this claptrap. Notice that there are many different kinds of PE and PP -- the chain length and exact properties depend on the manufacturing process.

 

Jack

 

Very nice response, Jack.

 

I'm not a chemist but I know BS when I read it. It's just another example of trying to sell "American-made" the wrong way. Why not be truthful: "Buy our American-made bags. The cost just pennies more but they keep American workers employed."

 

--Gary

[Tomega]

I prefer quadrotriticale.

[ShoNuff-migration]

PE is no better than PP. PP is no better than PE. They are different plastics but they perform the same service. Polyester film (Mylar) is basically the same - but is superior to PP and PE because it's thicker (except if it's a Mylite - then it's really no better - sorry, Kenny!).

Are you trying to say that the only difference between Polyethylene/Polypropylene and Mylar is the thickness? And that using the thinner mylar (mylites) is no better than using either PE or PE?

 

If so...sorry...but I'm not buying it.

 

That's exactly what I'm saying. If you're trying to person_having_a_hard_time_understanding_my_point the aging process, you need the right environment (cool, dark and dry). The bag will have nothing to do with it.

 

Mylites (polyester film) will not breakdown as quickly as PE or PP and retain their clarity longer, but they don't protect the comic book inside any better than PE or PP against storage and handling damage.

 

If you don't believe me, just ask the Library of Congress. They use polyester film (thick film - not Mylites) to protect their most treasured documents because it's clearer, thicker and stiffer than the other plastics - it's perfect for what they're main goal is - preserve, but make available important paper items.. But the environment that the documents are stored in is overwhelmingly the most important factor.

 

Mylites. Now that's good marketing. (thumbs u

 

That being said, I store my most important books in 4-mil Mylar. I don't use Mylites because they're just too expensive for the purpose they're used for (protecting inexpensive books). I prefer PE but also use PP.

 

I would never use Mylites on important, expensive books. They just don't protect well enough.

You mentioned that polyester film (Mylars/Mylites) will not break down as quickly as PE or PP. When material breaks down, it releases contaminants.

 

You also said that if you're trying to person_having_a_hard_time_understanding_my_point the aging process, you need the right environment (cool, dark and dry)...and that the bag will have nothing to do with it. I disagree here (in part) as well. While you do need cool, dark and dry storage conditions, if the bag used for storage breaks down, it will also have an effect on the aging process. Any cheap plastic with a thick backing board is capable of offering protection against handling damage, but that doesn't mean I'd want to store my comics in it, even if it was free and the books were being stored in optimal storage conditions.

 

The purpose of the backing board is to offer rigidity and protection against handling damage...while the bag is designed to hold the book and board in place while offering protection against outside contaminants such as dust, moisture, fingerprints, etc. So with regards to which bag is the safest for long-term storage of paper collectables without passively contributing to the degredation of it, polyester film is superior, regardless of its thickness.

 

Shonuf:

 

When I say that PE and PP "breakdown" faster, I'm referring to the PE turning filmy and yellowing and PP getting stretchy and wavy.

 

You can believe what you want regarding Mylar. As I said, I use 4-mil Mylar because it protects better than 2-mil PP, 3-mil PE or 1 or 2 mil Mylites. I've been in this hobby for nearly 50 years and started retailing in 1975. I've run across hundreds of thousands of comic books in every type of plastic bag imaginable. In all this time and all those comics I've never once seen a case where the bag caused any harm to the comic book inside. Even the yellowest, dirtiest, stickiest Baggie from the mid-60's had pristine books inside.

 

Just look at the threads that have popped up here lately for the nearly 30-year-old Gold Keys that are still "3 in a bag". Those comics are as glossy and beautiful as the day they were printed. The bags look like s h i t, but the comics are pristine.

 

I realized that I have some cheap books in my collection that have been stored in PE for nearly 25 years. I just checked them and the comics and bags are just fine (good storage environment obviously).

 

The evidence is overwhelming.

 

Bill Cole's marketing (along with Ernie Gerber's and yours truly) helped persuade collectors that they needed better protection for their comics than they could get using household products (Baggies, Saran Wrap). Bill and Ernie said that "cheap plastics" could cause harm to your books, and in the past 30 years millions of dollars have been spent trying to convince collectors that they needed more protection than they could get using cheap alternatives.

 

That being said, collectors (including myself) are proud of our books and want them to look as good as possible. Mylar, both 4-mil and Mylites, do make our books look pretty and that's probably the overwhelming reason these products are used.

When this same discussion came up a couple of years ago, I had several email exchanges with a preservationist at the U.S. Library of Congress, and this is not what was indicated to me regarding storage media. According to her, polyester film (mylar/mylite) is stable, and doesn't contain any harmful plasticizers, etc. that cheaper, less stable products contatin.

 

As I've already admitted, storage conditions (temperature/light/humidity) play a huge role in the preservation process. And while I don't doubt that you've seen a lot of books stored in cheap bags that still look good...this isn't proof that non-obvious and cumulative damage hasn't been done to the book. Simply eyeballing a book 30 years after it was printed isn't an accurate way to determine if the book has suffered any premature aging due to the media it has been stored in. Similarly, I know several smokers that could probably run a marathon and look very healthy, but that doesn't mean that the cigarettes aren't taking their toll on them.

[benz]

From what I know PP is clear as PE is "cloudy" looking. PE is more stretchable than PP. I would prefer PP over the clear factor as I can see the funny book cover pages clearly.

 

as to the protectiveness between the two, it should be about the same. It all boils down to the thickness, IMHO if they have the same thickness the barrier properties should be almost the same.