UKC

Whether worn as a midlayer or an outer, on the move or at the belay, this lightweight insulated smock is an excellent, packable companion to have on hand for all sorts of activities where only moderate warmth is needed, says John McKenna.

This looks similar to my TNF Zephyrus pullover. Mine is a bit warmer and heavier (the TNF is 40g of Primaloft One and 280g) and I used to use it quite a bit but I now miss a hood and don't feel I can snuggle down in it enough on belays. Always in the bumbag for a fell run though.

OMM Rotor is 230g and 40g of insulation. It’s light, but it’s not extremely warm. 
 

It’s not got the harness loop and packs into a pillow instead - I believe most races require it to be in a dry bag and that’s what it is designed for.