Novice “collector” – cards curling up as soon as I open them

Hey all – my og 151 binder got stolen 20 years ago. At the age of 33 my wife found a few mega kangaroo boxes and got me them for Christmas.

We decided to open one the other day for the novelty and it was just as I remember as a kid. Shiny stuff that nowadays I have no idea the value just enjoying the art.

I did have some cheap thin sleeves – but it appears they curled slightly. Mostly the holos/reverse holos. Is this due to storage climate or opening climate? I’m guessing the holos foil expands more or less than the rest of the card and something with humidity is involved but I’d just like to know if this is common and what I could do to prevent this in the future. As small as my little collection is it irks me to have them taco up 😂

Thanks for any advice!