I don't have the band anymore but it's Bernat handicrafter cotton twists.
I've used the handicrafter cotton before for dishcloths and I wash and dry those in the machine however they do shrink but go back to it's orginal size when wet, but with a bag I wouldn't want that.
So I think I should wash it and lay flat to dry (which if I am correct would be the time to block it) I've never blocked anything so this will be a first. How do you reccommed doing it? I'm also considering sewing in a snap button so I can open and close it.