Size One 6-18 pounds (see notes below, we think it runs smaller, 4-15 pounds or so) Size Two 18-40 pounds (we think it runs smaller, more like 15 pounds to about 30 pounds) The snap version is here: Thirsties Duo Wrap Snap. This cover has rise snaps. I think the size change from size one to size two might come at 15 pounds not the 18 pounds recommended but baby shapes vary of course, so weight recommendations are always a rough guess. Great over unpinned prefolds. Size one fits over newborn orange edge or novice green or small yellow edge prefolds. Size two fits over medium red edge, intermediate blue edge or size large brown edge Cloth-eez prefold diapers, trifolded and just placed in the wrap. If you need a cover to fit over size XL toddler prefolds, then you need the Thirsties Cover in Size Large or the even bigger Duo Wrap Size Three snaps instead. This is a no-pinning delight, but you can fasten the diaper underneath. They also work very nicely over Workhorse diapers and other fitted or fastened diapers, too. 100% polyester with TPU laminate FREE of VOCs, PVC, phthalates, lead, and latex. Made in the USA.