I buy this sleep sack for my 6 mo old baby . it be a good weight for the cooler spring evening , but be too heavy for daytime napping . I be a little disappointed with the size . the medium say up to 12 month , but my baby -lrb- who be 27.25 in -rrb- do not have much room to grow into it . I also find the armhole to be a little snug -lrb- my baby be in the 50th percentile on weight for she age -rrb- . all in all I think I would love this since I really like the fleece version , but the cotton version be not what I expect .