What exactly is it that causes a poster/paper to deteriorate? For example,I have two Italian posters from the 70s. One is in great shape, meanwhile the other is so brittle that it can hardly be unfolded without it tearing/falling apart. Is it the paper itself or the conditions it's stored in? Why is it that one is so brittle, yet the other one is fine? If it's the paper itself, is microchamber required for storage to prevent the paper from becoming brittle like that? Or is it just the conditions(heat/humidity) that must be controlled? If I can control the poster under the proper conditions, is it still necessary to provide for example microchamber paper as well to prevent it from deteriorating?