Mine looks and is the size of, 2 or 3 thick fine-weave black tee-shirts sewn one inside the other, zipped the long end, and elasticated sleeves. Pretty light and easy to roll up for a back-pack. I don't know the make unfortunately.
However its size means it's only good for 135/120 size cameras (to eek out those extra two shots on the beginning of the roll, or load IR film) and it's not big enough to change film in my 5x4 pinhole (opening the film box and taking out or exchanging exposed for unexposed) so doesn't get used often.
I've wondered about designing around the space I need to do that, getting the material and asking a needle gifted friend to sew one up for me. There must be some black kite-fabric-like materials, light weight but light proof out there. I'll watch any tips that are are posted too.