My curiosity got the better of me. So, I e-mailed John Gookin, explained the context of my inquiry, and he was kind enough to reply today.

My question: "We're of course familiar the concept of heat loss through the head, but special mention of the eyes (and sunglasses) piqued our interest. Could you provide a brief explanation of the dynamics: Why the eyes? Why sunglasses?"

Mr. Gookin's reply: "I've spent quite a few nights out with no sleeping bag. Most were as a recon marine. Some were as a SAR person who got my patient flown out but ended up waiting a day for my own ride out. Others were as a mountaineer in bivouac mode.

When I just have what is in my daypack, or pockets, anything I can do to cover bare skin makes a detectable difference in localized skin warmth. It just feels more comfortable than without.

I don't think there is anything about the eyes in particular, other than being on the head which doesn't shunt blood flow like the extremities do.

BTW, I also often use my spare socks over my hands."

I'm guessing that sunglasses were specified only because more people are likely to carry sunglasses as opposed to just (prescription) glasses, and that non-tinted glasses would do just as well.

While researching, I found that John has an impressive résumé, including: active in the National Speleological Society and Wilderness Medicine Institute; extensive cave-related and general SAR experience, instructor and curriculum manager for the National Outdoor Leadership School, author/co-author of several related books, and time spent as a Recon Marine.

Dan