The fabric is very soft and stretchy, which makes it a little easier to dress a very wiggly baby, but not very warm. The vent in the back is more for looks than usefulness. but that gives it the old world style. My son has worn this several times but it appears the knee area is starting to wear. My son is 23 lbs and 10 months old, and the 12-18 month size fits him good. May last a little longer in size b/c of the stretch.