The Yellow Unicorn Adult Onesie is 95% cotton and 5% spandex. This allows the onesie to stretch, which is great for wearing with nappies. All cotton based products can shrink up to 10% when washed for the first time. Measurements are taken with the item laying flat. Whilst we do our best to ensure measurements are correct, there maybe slight discrepancies. Comes with short sleeves, and 3 snaps at the crotch to allow for easy nappy changes.