This is the BEST PJ on the market today. It features Super Soft 100% Thermal Cotton. The PJ has fantastic stretch which makes it very comfortable to wear and easy to put on. We embroidered the bottom with "Sweet Dreams." It also features an OPEN TAIL END for quick potty breaks. Sizing Information: X-Small: Chest 10-12" Neck 7-10" - Pets weighting 3-5lbs. Small: Chest 13-16" Neck 10-13" - Pets weighting 6-10lbs. Medium: Chest 16-19" Neck 13-16" - Pets weighting 11-15lbs. Large: Chest 19-21" Neck 16-19" - Pets weighting 16-32lbs.