Any question worth asking has already been posed to the Yahoo! Answers community. For example, in the winter, when it's snowy and freezing and waiting for a bus or driving a car calls for some warm fingers, Yahoo! Answers asks: Why are mittens warmer than gloves? The answer is simple science, really. It's all about surface area. But what if, even in the face of science, you reject mittens for gloves because you need to keep you fingers flexible? BoingBoing suggests you wear glittens.
What are glittens? Glove-mitten hybrids, obviously. They sound slightly freakish, and they look a little weird, too, but warm fingers may be worth paying that price.
The scientific justification for gloves-that-are-also mittens: Gloves give each of your fingers free reign to wiggle around inside their insulation (yay), while mittens turn your hands into cozy-but-basically-useless lumps (boo). And that's why mittens are warmer. Heat transfer naturally conveys warmth from a warmer object to a colder one. Open a window in your heated room, and all the warm air rushes out to create equilibrium. Walk outside in the cold, and exposed fingers will radiate their heat away. Hand coverings put a barrier in the middle of that heat process, so the glove itself retains some of that warmth before giving it up to the cold.
Gloves expose far more surface area to the elements than mittens, since each finger is protected individually. With more expsosure, fingers lose heat faster. They also can't rub up against one another to share their heat, which they can do in mittens. Advantage: Mittens.
Glove-mitten hybrids usually cut finger coverings off at the knuckle to provide the flexibility to manipulate a phone or handle money, but they also include a folded-back covering to slip over those exposed fingertips and turn the gloves into oh-so-warm mittens. There are even some high-tech versions, like the Nathan Transwarmer Convertibles, with capacitive touch fingertips and a little pouch on the back of the glove to store the mitten covering. They also have have LEDs embedded in them, in case you're afraid of the dark.
Heat Factory calls them Pop-top mittens, which is at least as good a name as glittens. We'd also be okay with glottens, but the mittens deserve most of the credit here--they're doing most of the work to keep your fingers warm, and most glove-mitten hybrids tend towards the mitten end of the spectrum when it comes to materials. If you love woolen mittens, woolen glittens will probably be a revelation.