(This article is going to evolve more with input from members, so feel free to comment)

Most people will tell you that "mittens are warmer than gloves".  While that is the case most of the time, I cannot say that gloves are indeed colder than mitts.

Remember, no piece of clothing is actually warmer or colder than any other piece.  We say that something is "warm" if it has the ability to retain our natural body heat in a comfortable way.

For clothing manufacturers, hand coverings are especially challenging compared to other wearables.  They need to be tough and durable yet still provide the dexterity the person needs.  This is why a GOOD pair of gloves (or mitts) can cost the same as a nice jacket or pants which are many tomes larger.  The challenge is no longer in the fabric itself, thanks to waterproof/breathables (like gore-tex) and now they are even making these technical fabrics in "stretch" that allow for more mobility!

The real challenge is in the SEAMS.  To get the shape of the hand, with all four fingers and opposing thumb, many seams are needed.  This means punching hundreds (if not thousands) of little holes into the material, and creating many potential points of failure -- both on the level of structural integrity (holding together) and performance integrity (remaining waterproof and breathable).

The ability for a hand covering (or any covering) to keep you "warm" is to be able to do the following:

1) Create a "micro-climate" inside.  An ideal micro-climate is one that keeps the elements out and keeps moisture levels minimal.

2) Maintains blood flow through the area of the body.

If any article of clothing can do the two things mentioned above, it will be "warm".

Back to mittens vs. gloves, this is why mitts are so many times better than gloves.  Most gloves will fail in one of these two areas:

1) The glove will not be properly designed.  It may not be made of the proper materials or they may not have taped seams.  They also may have been fine when new, but after some wear failure occurs somewhere.  Mitts have so many fewer seams and thus much less chance of failure.

2) The glove  restricts blood flow.  This is all too easy to do since the numerous seams of a glove are on the inside, taking up room.  Add to it all the additional insulation that envelopes each finger on all sides and you have a recipe for stifleage of flow.  No beuno!  It is the body's blood supply that actually keeps things "warm" inside and even the slightest pressure anywhere around the hand can be restrictive.  Mitts simply have much less chance of doing this.

So are mitts really warmer than gloves?  Not necessarily.  If you have the right glove for you you can rock em on the coldest of days.  (Lucky me, I actually have a pair!)  But I like mitts too, so personally I don't have a preference.

I hope you find this information useful, have fun on the SNOW ***

my hands feel warmer in mittens because my fingers are together and keep each other warm (and happy)

Good point Rowan, i will have to add that into the article.  Also, the factor of material insulation.