These gorgeous covers are made with 2 layers of soft breathable Austrian double-knit wool serged with elastic at legs and waist for a super soft diaper that is super trim for day and works for most children for overnight (as long as there is enough absorbency in the diaper underneath). This wool is nice and stretchy so it provides a great snug fit. Side snaps allow for independent waist and rise adjustment with good coverage over any diaper. Small fits 8-16lbs Medium fits 14-26lbs Large fits 24lbs+