In my 30+ years of experience of working outdoors, mountaineering, ice climbing, backcountry skiing, and winter biking in Canada, often in temperatures down to-30 Celsius, I’ve spent a lot of time trying to find the right gloves. By far the best gloves I’ve ever used have been high-end ice climbing or mountaineering gloves. You’ll pay a steep price to be sure, but the reward is substantial.
They need to have a full box construction in the fingers to prevent even the slightest restriction to blood flow. Even the tiniest bit of “snugness” anywhere in the knuckles or fingers will restrict blood flow enough to turn your day into misery. They are pre-articulated and have a more pliable fabric on the underside for easier gripping and have a grippy texture for holding tools. Some also have knuckle padding too. They often also are offered in a wider range of sizes than the typical S, M, L, XL to get just the right fit. Try on as many pairs as you can find. Ones with the inside liner than has a fleece fabric with Gore Windstopper fabric are best and I’ll often use just the liner without the Gore-Tex overglove down to about -8 to -10 Celsius. Below-20, things tend to get a little more uncomfortable no matter what, but still not likely to get into frostbite territory.
Also your cockpit setup is critical… any pressure points on your hands or wrists will restrict blood flow. Winged grips like the Ergon GA3 help a lot with this (I use them year round on all my bikes). If you find yourself getting any amount of numbness from your setup during summer rides, you need to change up your cockpit to eliminate that. That’s a whole other complex topic though.
These are my favourites (kinda smashed flat from summer storage)…
View attachment 129423