Breathing Bags - 

These bags allow the transfer of simple and complex gas molecules through the plastic wall of the bag -- carbon dioxide and oxygen in particular. 

The plastic is very tough, yet flexible. 

The thickness is 1.5ml for the smaller size and 3ml for the liner bag.

Can be used in transportation or shipping of fish or plants (which transpire just as animals do).

Kor81: 4" x 8"