Is there a difference between Mylar/Prolar Polyester/Generic Polyethylene Terephthalate holders?
airplanenut
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Edit: I hope this is useful for someone in coin land, but I apologize... I meant for it to be in the currency forum. If you're wondering why my references are to currency, that's why. My bad 
I asked a question about currency sleeves a little while back, so apologies for starting a new topic. I know that Mylar/Melinex are DuPont brand names. Frame-A-Coin sleeves are advertised as being made of this material. Other brands, namely Safgard and Supersafe, list Prolar Polyester or Polyethylene Terephtalate as the material. In a broad sense, these should be just about the same material if not the same. If they all are the same (or any differences are negligible) I'll just buy what's most economical. If true Mylar is the best of the best for whatever reason, I'm willing to invest more for the best product. I've found some discussions of the materials when searching, but nothing conclusive. Can anyone here provide some guidance?
Comments
Mylar is a brand name for PET. Either is the best material for coins.
As far as I remember, Frame-A-Coin used hard PVC (the kind that doesn’t off-gas much, so is supposedly safe). It is ok, but not the best material to use. All the cheaper “safe” brands also use hard PVC.
The only company making coin flips in PET is E&T Kointainer Co (the Saflip and Safgard brand). This is what PCGS uses.
Polypropylene is also safe and is often what archival albums are made from.
As with most things chemical, the problems don't usually come from the "main ingredient" - they come from the minor components. We all know "PVC is bad", but it isn't the actual polyvinyl chloride that causes damage - it's the sulfuric acid retained in the phthalate plasticizer they add to cheap PVC that causes the damage. If there's no acids or phthalates used in the manufacture, PVC is "safe" - but "raw" PVC is also not very suitable for coin albums, being brittle and not entirely transparent. Effective alternatives to phthalates are expensive, so it's usually cheaper just to switch to a different plastic that doesn't need additives to be useful for coins.
Any plastic can be "safe for coins", and any plastic can be "bad for coins" - it all depends on the other chemicals they've used to make the plastic. The cheap, generic, made-in-China stuff? As with everything "made-in-China" these days, the quality control is completely unknown - so you really need to test it first before trusting it. Unfortunately, without access to a chemistry lab to do some analysis for you, this will mean field testing: putting some nice shiny coins in them and leaving them there for several years.
Roman emperor Marcus Aurelius, "Meditations"
Apparently I have been awarded one DPOTD.
And this is really the crux of the question: Mylar is a DuPont brand name, so if it has been shown to be safe, I trust that. Perhaps the question for the Safgard and Frame-A-Coin products is whether their version of PET (the whole of the product, including the secondary ingredients) is known to be as safe as Mylar. If so, then ostensibly they all serve the same function. If not, then sticking to a product made of the known DuPont material seems prudent. I'm certainly not considering any of the very inexpensive options--those quite clearly have red flags, just as I stay away from any soft flip for long-term coin storage (though my coins are almost entirely graded, so it's not much of an issue).
Both Saflip and Safgard are only incrementally more expensive than other, untested, products. Given that coins and notes are so expensive now, why take the chance using inferior products?
Frame-A-Coin isn't Mylar/PET, but unplasticized PVC. They claim it's archival, but it isn't and museums do not use them. And BTW, they used to be made in Madison, NJ. Then they moved elsewhere, though I believe they are still made in USA.
When I was a noob, I ordered cheap currency pockets from (I think) Brooklyn Gallery. The plastic had actual black impurities in it that could be seen while looking through it. And the box was some flimsy junk that screamed Made in China. Lesson learned. Now I only use E&T Kointain products and Itoya albums for my currency and proofs.
For large medals, Ziploc bags are actually a good archival material too. Get the thick freezer ones for better protection.
This may be where my goof of posting on a coin page instead of the currency page (as intended) may show. Frame-A-Coin does make a currency holder specifically advertised as DuPont Melinex, but I don't think they make a coin holder of that material.
Mylar has less gas permeability than polyethylene, polypropylene, and some other commonly used plastics. That does help to keep the environment out and improve preservation. That being said, polypropylene can be perfectly acceptable. I would be reluctant to use any plastic longer than 50 years. Some of the older US mint packaging and even some TPG holders are getting long in the tooth and warrant replacement.
IG: DeCourcyCoinsEbay: neilrobertson
"Numismatic categorizations, if left unconstrained, will increase spontaneously over time." -me
I'll put a note on my calendar to post a follow-up in 2073 asking if there's a new, better material to switch to
I've always assumed the soft UNC set packaging was... cellophane. Which isn't even "real" "plastic"????
So much chemistry...
This is not really the question and not all that scientific, but on the topic of inert "things that won't eff up your stuff"...
I shop, open, and drop a ton of coins. Basically, quick look, everything OK?... I want to stick the piece in something and forget it for a while. Old fashioned cardboard/mylar 2x2s seem to retain moisture in damper conditions. Soft vinyl flips (plasticized PVC) of course make the ruinous goo... the cheap inert ones (UNplasticized PVC) are best used for slicing open human flesh and harvesting kidneys (and also scratching coins). As pointed out above, too brittle.
Saflips (PET) are good and inert... BUT it's still an open flip, so the coins will look to tone nearest the air exposure. And, ALSO can be used for the flesh slicing/organ harvesting.
All of this bothered me... thought about finding the nearest cliff from inability to deal...
After some searching, figured out that they make polyPROPYLENE "zip-lock" polybags. NOT Polyethylene (AKA ZipLoc material and normal 2x2, 2x3, etc. jeweler/illicit street drugs "polybags")... which is supposedly inert but reality is coins with haze over time. They are wonderful and cheap for quick, no think/no worry storage. Everything I've put in them over the past... IDK, 7, 8 years??... looks exactly the same. Somehow, the zip-close is solid, seems to be pretty damn near airtight - even on this less pliable form of plastic.
The zip-lock feature is important. The plastic debate is great, but has to be combined with a discussion of keeping air /moisture away. I don't want my coins toning when I don't want them to!
Oh, and btw, never ever ever use rubberbands around anything collectible (or around kitties, who like to eat them).
What did the famous collectors of old do with their coins?
They kept them in trays, made of uncertain wood, stored in the open air in a men’s den or smoking room, probably with gas lighting, candles, and fireplaces burning.
And you know what, we all loved the resulting look of those coins!