why are they out of their boxes? how long are you leaving them in the bed? what brand are they? I think the card board boxes actaually helps alot with heat!
I've left my Evils on the sun for a while and they worked ok…..
paintballs will always tend to shrink in the summer and swell in cooler/wetter conditions…
Its that foam as a bed liner? if it is…. thats a good Ball protection Mod…lol