crisp bag

[homedeeth]

when you scrunch up an empty crisp packet or similar how/what/why does it increase in size again? what's it trying to do?

[Clanad]

Doesn't have to be a crisp bag (or our potato chips here in the U.S.) it can be any fabric. However, modern packaging, especailly of foodstuffs that require protection from light and air are usually made from polymer resins and are often overlaid with an extremely thin sheet of aluminum (aluminium to you Brits). Polymers are chains of molecules that want to fold into each other, but when heat an pressure treated, they're stretched into sheets that cause the fabric to have a "memory". It's this characteristic that causes the scrunched up bag to attempt, to a greater or lesser degree, to return to it's original shape and size...