Pajama Dress is made with 95% Polyester and 5% Spandex. The fabric is a soft & silkier texture. These are designed to be a tighter fit. Please plan to size up if you want it to last your little one a longer time! 

Refer to the sizing Chart for wide of dress. This is from armpit to armpit
(one side only; make to double the measurement for full circumferance)
12-18M: 10 inches
2T: 11 inches
3T: 11.5 inches
4T:  12 inches
5T:  13 inches