The Java Filter is an ultralight way for you to get the quality coffee you enjoy at home but out on the trail. This is a spare for those well used GSI Java filters.
GSI Outdoors says:
Say goodbye to single use coffee filters. The GSI outdoors Reusable Java Filter #4 is designed to brew coffee or tea over and over. Easy to use and clean. Durable Nylon. Designed to fit into traditional #4 cone pour over coffee makers.