When you first try on the Black Diamond Mercury Mitts, you might find yourself slightly confused. Your hands will be so toasty warm that you'll swear the gloves are generating their own heat. You'll pull them off again, separating the liner from the outer, turning them inside out, looking for chemical handwarmers stuck in there by crafty salesmen or for electronic heating elements. Then you'll come up empty-handed (no pun intended) and come to the only possible conclusion: the Mercury Mitts are made using some kind of arcane witchcraft. And you wouldn't be far wrong.

These things are LUDICROUSLY warm. That's the overriding impression they will leave with you. But there's a lot more to them than that.

The Mercury Mitts are a two-part system and that warmth is mainly due to the generously insulated inners. They feature a thick wad of Primaloft One insulation across the back of the hand and a full wrap of Primaloft Thermal Pro Hi-Loft fleece wrapping all the way around. This keeps your entire hand toasty without impeding dexterity too much (within reason - these are mitts!). Dexterity is further improved by the inner's design - they have a 'lobster' design with a separate index finger. Even used inside the outer shell, this helps to make things a little easier to manipulate. The inner also features a BDry insert, which is fully waterproof. It seems to breathe pretty well - I've never had particularly clammy hands, even in relatively mild temperatures.

The inners fit nicely inside the outers and are held in place by a thin strip of velcro around the cuff. This works just by putting the inner inside the outer - no messing around trying to seal things up!

The outers themselves can best be described as 'beefy'. They're made of a very robust-feeling nylon shell with a thick yet supple leather palm. There is an extra layer of leather in the crotch of the thumb and index finger to help stand up to the rigours of ropework and abseiling. They feature a one-handed cinch tape around the wrist plus elastic on the bottom, meaning you can whip them on and off without having to loosen them off each time. Around the cuff is an elastic drawcord, again one-handed in operation. Also attached within the cuff is a decent wrist loop with cordlocks. Also of note is the hang loop on the top of the outer, above the fingertips, which allows you to hang the gloves from your pack/harness without them filling with snow.

I love these things as belay mitts. They're toasty warm, they'll keep you dry and they offer good grip and surprisingly good dexterity. I sometimes use the outers on their own over my ME Randonee gloves at belays and keep the inners as emergency gloves or for around camp at night. The gloves are so well designed that you can comfortably climb in them - there is little slip between inner and outer, meaning even leashless tools handle quite well.

If you are looking for a pair of big, beefy mitts for cold conditions, look no further than the Mercury Mitts!