They're lined with nylon and feature velcro closures. When you're done using them, just flip them inside out, closing the velcro and toss them in the washer. The little bags, available in a variety of cute prints, have gussets so that they will stand up on their own.
I think they're terrific to bring nuts and healthy nibbles to snack on at work. I gifted a mom of young kids with a set of these and she's gotten rave reviews from the other parents at her preschool.
In addition to the nifty snack bags, Mosquito Lodge also sells some handy iPod Touch covers and the sweetest lavender sachets you'll find anywhere!