It’s a fact – metal brake handles are colder than plastic ones. Ask anyone who rides various brands of sleds, and they’ll all tell you that a sled with a metal brake handle will suck the heat out of your left hand far quicker than a plastic one. Think of it like a “heat sink” in reverse, the metal draws the heat out of and away from your glove and hand, dissipating it.
One solution we’ve seen some riders use is to rubber-dip their aluminum brake handles, giving it a coating that insulates the metal from your hand. Riders who keep a finger or two on the brake lever most or all of the time will notice this far more often and to a greater degree.
Why do some OEMs use a metal brake lever instead of a plastic one? It could be due to the greater control over the exact size and dimensions of the lever; it could be due to aesthetics (appearance); it could be due to uniformity and strength. Other than the heat-robbing nature, it is the superior method for the application.