The U.S. Navy is working on a unique way to
keep its divers warm — a layer of foam containing
bits of wax inside tiny plastic beads, each just
a tenth the width of a human hair. These bits of
wax melt and freeze as the temperature
changes. While the diver is putting on the
drysuit, the wax absorbs warmth from the
diver’s body and melts. Then, when the diver slips into the icy waters, the
wax freezes, radiating latent heat back to the diver.
To provide optimal warmth to the diver, the wax must melt at a
temperature below that of bare skin — about 92° F. Similarly, the wax must
freeze at temperatures as high as 65° F. to provide enough heat to the diver.
So far, the warming effect lasts for about the first half an hour or so of
the dive. However, the Navy hopes to improve on that by packing more of
the wax into the diving suit liner or weaving the beads into layers of
synthetic fabric instead of foam. Another way to extend the warming
capacity could be using a combination of waxes that freeze at different
temperatures, so that heat is released gradually as the temperature drops.
The beads, which look like fine dust, can be placed inside fabric fibers
by mixing them with the liquid polymers used to make artificial fibers.
Catherine Zandonella, New Scientist