I've got a pair of the specialized defrosters, and although they're pretty warm down to about 30F, or upper 20s, once in gets down into the teens (as it finally has) they are no longer very warm (even for relatively short periods of time). But what i've noticed is that most of the cold seems to be coming in through the bottom (but not just the cleats). When I stand on the cold ground it's very cold on the bottom of the shoe, especially the heal and the arches.

I was wondering if there are any ways to improve the warmth of the bottom of a shoe. Thermal insoles, some other type of DIY insulation? Any experiences?

The shoes are otherwise pretty damn warm (that is they don't seem to lose a lot of heat from the top despite their minimal insulation), and are big enough for a REAL thick sock (or some more thickness on the insole). And they're completely water proof - thus far at least.