The Expander™ sleeping bag liner is a super soft and stretchy poly-cotton making it wonderfully stretchy and warm. It's an ideal choice for travel, car camping and any activity or adventure where you want to keep your sleeping bag clean or add additional warmth to your sleeping bag. The 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 if you're wanting a luxuriously comfortable sleep.