In reply to henwardian:
Mine works great over a helmet, however I did size up from medium to large on mine to fit over layers easily, and also it’s easier to share it with people who are taller / bigger than me.
I believed they were made for winter climbing so are a good active fit, and you can unzip from the bottom to expose belay loop, however I think they may not be warm enough for true winter climbing belay duties, but for an emergency hill walking outer and for bouldering and trad belaying in the uk winter they are fantastic.