Arm Bag

A large ‘bag’ generally made to cover casts when bathing.  Includes straps to seal the end.

Don’t seal so tight it cuts off the blood circulation.  It’s good to allow some gas to escape so fresh gas comes in.

Fun fact: They are also available in most local pharmacy or online.  Or at most farm feed supply stores because they are used to protect the arm when inserting it into large animal cavities… :)))
I know this because I grew up on a cattle ranch.