The material is 95% polyester and 5% cotton. There is stretch sideways, but none length wise so pay extra attention to length! Please measure and check the size chart to get your correct size! The unit is in inches.
Please also keep in mind that the sizing is different than other onesies in this shop! They fit extremely small. I switched manufacturers and made sizing adjustments, so it is likely you will need to size up 1 or even 2 sizes. I highly suggest sizing up 2 to be safe.