Baby onesies are designed most often in 100% cotton. This fabric is thick, yet lightweight and breathable. It is comfortable and soft, so it won't irritate your baby's delicate skin. Cotton washes and wears well, is strong, and doesn't typically rip or fray.Some other onesie baby can be made from Muslin cotton, a different variation of cotton. It too is lightweight and breathable, and it gets softer with every wash.You can also find cute baby onesies designed in a cotton blend, which can be mixed with rayon or polyester, giving it ultimate stretch and making it a wonderful layering item.As mentioned before, onesies can be organic, colored using natural dyes. They can be all kinds of colors, prints, and patterns. However, onesies are most popularly picked up in a plain, white color so they are versatile enough to wear with anything.