Chemical Warming Blankets
I just came across this product, chemical warming blankets, for the first time. I thought it might be worth sharing.
These products (blankets, vests) seem to be a scaled-up version of chemical hand-warmers. Opening the packaging and exposing the product to the air triggers the chemical reaction and heat. The product warms up to 100°F / 38°C in 10-20 minutes, and gives off heat for 8 hours.
Possibly not the greatest idea for those at immediate risk for afterdrop... I have no medical background, but I suspect the blanket version could trigger vasodilation in the limbs and speed the flow of cold blood to the core.
However, they do have vest-only versions that might help swimmers warm up their cores, or could be helpful to crew standing in a cool breeze all night.
Possibly highly useful in the right situation.