I'd suggest going for something a bit thicker than a 100gsm fill synthetic for long belays in the cold. 100gsm has got me through some trips in Oz, but I definitely was happy to have my 200gsm jacket when I was ice climbing in Canada during March. If you want to keep the weight down by sticking with 100gsm, then don't skimp on the fill quality, and buy a jacket with Primaloft One fill, rather than Primaloft Sport or Eco.
Check out the Rab Photon Belay Jacket. 200gsm in the body, lighter fill in the arms and hood, and a very water resistant outer fabric. This is what I have, and I really like it. Don't buy a belay jacket without a hood that fits over your helmet, you'll spend a lot of time regretting it.
As for sizing, I'm also 180cm and 80kg (well 79 or so) and I got a large. It's too big, a mate has since purchased a medium, and it fits me much better, so thats what I'd suggest for you.
Anyone who stocks Rab should be able to order it in for you, even if they don't stock it. Something with that much fill and the good outer fabric isn't cheap, from memory, the Rab belay jacket retails around $450 in Oz, but I love it. Highly recommended. I've used it ice climbing in Canada, and my core was never cold, despite the ambient temps and long belays, and my mate used it heading up Lobuche East in Nepal, and likewise, he was never cold. |