The Napsac has been discontinued. If you're looking for something new, check out the best sleeping bag liners for 2020.
Altrec Outdoors says:
Made from a breathable and fast-drying cotton/polyester blend, the Napsac Sleeping Bag/ Liner from Eagles Nest Outfitters is great for travelers who are going light on a budget staying in hostels, need light coverage while sleeping in hot climates, or want added protection for their sleeping bag.
Historic Range: $54.95