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