The Expander™ sleeping bag liner is made of a super soft and stretchy knitted poly-cotton material. The Rectangular, Traveller and Double models do not have side seams, and combined with the stretch fabric, this offers an unprecedented level of comfot in a budget-priced liner. A built-in antimicrobial treatment keeps odors at bay and won't wash out of the liner when you throw it in the washing machine. This is the perfect travel companion for those looking for a luxuriously comfortable sleep. Assorted colors.