[waqf]

Is that effect mediated by body size, or is it true even when corrected for body size and shape?

[piva00]

It is directly affected by body fat at least. Fat is insulating (hence whales, seals, etc. having a thick fat layer) and definitely being on the larger size with a higher % of body fat makes someone feel warmer.

[bearmode]

It's also directly affected by muscle mass, for a similar reason. Also body mass to body surface area does play a part from what I've read.