Well, to explain it in molecular terms, all the items or objects or even ourselves are made of atoms. Usually inbetween atoms, there is something to fill in the gaps. For solids, atoms are paired very closely. For liquids, slightly apart. Gases, even further apart.
So the space inbetween atoms are usually filled with air or water, or some other molecules. For natural substances like rubber, it was once in a liquid state, and there were some water molecules inbetween the rubber atoms. So when it was made into solid rubber, some water molecules, or in lament terms moisture is still present in the solid rubber. This is why some solids can flex and twist and some cannot.
So from long periods in a dry box with very low humidity will slowly dry up the moisture. So these items cannot flex and twist very much. Thus you have rubber peeling, and stuff like that. You can try it out for yourself. Get a piece of rubberband, put it in some silica gel, after a few weeks take it out. You can practically break he rubber band. It's not longer elastic or neither it can twist or flex.
Now the biggest irony, is that me knowing the answer, i still leave my dry box at 25% RH.... Haha...how dumb can i get.
Hope it helps, but do note, my explaination might not be very detailed.
GMAN
