Will Wittman Folders Hurt Coins?

NONE of the "folders" or "albums" are airtight.....so it then boils down to "storage environment".
Whitmans folders will be just as good as anything else unless you store them in a bad spot....high humidity.....temperature fluctuations.....other "coin toxic" air conditions can and will eventually "affect" your coins if left exposed to these anti-hospitable coin conditions.
The best most expensive albums with protective sleeve sliders etc. etc......will NOT protect/prevent "bad environment" conditions from ruining coins.....
So, just wrap these Whitman folders in ziplock bags.....or some use aluminum foil....or pvc free containers....or safety deposit boxes at the bank.....or safes with humidity devices......whatever.......but some sort of "protection" beyond just the "folder" would be advised......even though the coins are reletively inexpensive "pocket change".......if they get ruined...then you've wasted a lot of time. Whoever inherits this collection/work of yours, will not like to see "spotted/corroded" coins in 40 years or or even next month......doesn't matter......protect them babies !!...

I agree that environment is a huge factor. If the albums perform better, I would say it has to do with their limiting (not preventing) air movement (since both sides of the coin are "protected" with the plastic slides). One cannot forget about materials; a lot can be said about the adhesives used in folders.

That said, I still have my old Whitman folders tucked away. I put a bunch of coins in them not long after I moved my good ones to Dansco albums. I got them out this weekend to take a look at them. They have fared much better than one might expect. I did not look at the backs though.