Soft Flexible Real Rubber , easy to stretch
Small ,     Top opening is 2 5/8"   Bottom opening is 5 3/8"
Medium , Top opening is 3"          Bottom opening is 5 1/2"
Large,      Top opening is 3 1/4"    Bottom opening is 6"
Xlarge      Top opening is 3 1/2"    Bottom opening is 6 1/8"
XXLarge   Top opening is 3 5/8"    Bottom opening is 6 3/4"