The material of these is very lightweight, yet seems to keep the baby warm. Or, conversely, keeps them cool when the weather is a bit warmer. (Yes, I went in to check on the baby while he was sleeping, in both warmer and cooler weather, and he always felt okay temperature wise.) That said, I do wish they made these with feet (bigger sizes of the&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/Halo-Technical-Comfort-System-Coverall/dp/B0029F1K7G/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Halo Technical Comfort System Coverall</a>, please!) as it does get REALLY chilly here during a northern Michigan winter, and I honestly am not sure I would put my baby to bed with uncovered feet. That said, I can just put a pair of socks on. These jammies also wash very well and the boy is so cute in them!

Edited to add: My son is now 27 months, 40 pounds, and almost 40" (yes, he's a big boy--in the 100th percentile) and he's just now starting to grow out of the 24mo set!