It's not a rookie mistake. UltraPro collectible card holders are perfect and I've had my HuCards in them for almost 20 years now with zero issues. Just don't stick them in soft credit or business card sleeves. I think that some of the HuCard binders from bitd might be risky as well.
I use 4-card sheets, which are already pushing the limit for ease of leafing through.
Well thank you for the reassurance. I have a lot of these as I have still yet to purge my bins of collectible cards from my youth (maybe there are some loose hueys in there!! cant toss the bins without sifting!) so I was considering using them, I am fairly certain that they are UltiPro brand, as I was pretty into NHL cards in the 90, and had some binders of things I hoped would be valuable. Maybe I will put a keith courage in one and leave it in a warm part of the house for a while, see what happens. Test card