DuraTherm is fiber-reinforced ice: cotton woven through frozen water, based on Pykrete, a material first developed during World War II. In a 14-hour infrared test against 27 standard gel packs, no DuraTherm pack reached the out-of-range line, and DuraTherm warmed at half the rate.
DuraTherm overview
Ordinary ice and gel packs sit at or below 32°F at the surface until they warm unevenly, cold in one spot and warm in another. Too cold can injure skin; too uneven means the product or the patient gets inconsistent cooling. The options until now have been towels over ice, costly phase-change packs, or powered cooling machines.
DuraTherm uses long fibers to restructure the ice. The fiber holds the water in place and changes how the pack melts, so the cold spreads evenly across the whole face and lasts longer. It is low cost and simple enough to send home with a patient.
0 of 23DuraTherm packs ever reached the 70°F out-of-range line
10 of 27standard gel packs were at or above 70°F at the 5:00 a.m. read
½ the rateDuraTherm warmed 0.86°F per hour vs 1.68°F for gel packs (3:00–5:00 a.m.)
2.8°F colderaverage surface at 5:00 a.m.: 66.7°F vs 69.4°F
Uniformity. Across 40 measurement rounds, DuraTherm demonstrated approximately 53% greater pack-to-pack temperature uniformity than conventional gel packs, with lower temperature variation in every round.
Where to go next
Summary: the one-page version for busy readers and investors.
Science: how fiber-ice works and what the infrared data shows.
Documentation: the full test protocol, pack inventory and data files.
Business: markets, manufacturing and how to get involved.
Sixty-two packs came out of the freezer at 3:00 p.m. and were imaged with an infrared camera from 4:00 p.m. until 5:00 a.m., a 14-hour run. Every DuraTherm pack was built inside the same commercial gel-pack shell used for the controls, so the only difference was what was inside.
Medium packs
27 standard gel packs and 23 DuraTherm
Small packs
6 standard and 4 DuraTherm
Large packs
1 standard and 1 DuraTherm
Setting
R-6 insulation board, still air, room near 73.6°F
Readings
rear face only, five zones per pack plus the whole face
8:45 p.m., about six hours out of the freezer. The typical pack of each type (the median of 27 gel packs and 23 DuraTherm packs by center reading), shown on one shared five-color temperature scale. The gel pack has a single cold pocket and a warm body; the DuraTherm pack is cold across its face. Group center readings at this time averaged 45.1°F for gel packs and 40.9°F for DuraTherm.Evening, 4:00 to 8:45 p.m. One typical gel pack (26MC) and one typical DuraTherm pack (11MD), straightened and trimmed to the pack outline, converted to real °F and recolored on one shared five-color scale (30–60°F).Overnight, 1:30 to 5:00 a.m. The same two packs, straightened and trimmed to the pack outline, on one shared five-color scale (59–74°F). Face averages are printed under each frame.
The overnight numbers
Standard gel pack (27)DuraTherm (23)
Average whole-face surface temperature of the 27 gel packs and 23 DuraTherm packs at each overnight read. The dashed line is the 70°F out-of-range line. Hover a point for its value.
Standard gel pack (27)DuraTherm (23)
Number of packs reading at or above 70°F at each read. DuraTherm had none at any read.
Bulging. In the heavy-fill DuraTherm variant tested on October 3, the gel packs had spiky bulges, while DuraTherm had controlled bulges spread across the whole pack. Older legacy DuraTherm units with lighter cotton fill did not show the same level of bulging.
Pykrete: the idea behind DuraTherm
Pykrete is frozen water reinforced with wood fiber. During World War II, Geoffrey Pyke proposed building an aircraft carrier out of ice for Britain's Project Habakkuk. The scientist Max Perutz, working in a cold room under London's Smithfield Market, found the best structural mix was about 14% wood pulp and 86% water.
The fiber changed how the ice behaved. Pykrete was much stronger than plain ice: in one demonstration, a bullet shattered a block of ice but bounced off a block of pykrete. It also melted far more slowly, because the wet fiber on its surface formed an insulating shell that protected the frozen interior. A prototype was built on Patricia Lake in Canada in 1944. In 2009 the MythBusters built a working boat from a newspaper-based version.
From warships to cold packs
Pykrete has been studied, demonstrated and built for more than 80 years. Nobody had applied it to medical and cold-chain cooling. DuraTherm takes the same principle, fiber woven through frozen water, and tunes it for a different job: holding a controlled cold above freezing, evenly across the whole pack, for longer.
Pykrete's goal: strength and slow melting for a structure.
DuraTherm's goal: an even, controlled surface temperature for the person or product being cooled.
The fiber: DuraTherm uses cotton, a long, clean, well-understood fiber that holds water by wicking.
Sources: the Project Habakkuk history (Wikipedia, "Project Habakkuk"), and MythBusters, 15 April 2009 episode.
Earlier tests
Test #1: fiber ratio
Eight cubes: seven with fiber and one plain-ice control. Cubes at 2.9% and 5.8% fiber by volume behaved much like ice and eroded within three hours, like the control. At 8.7% fiber the cube held 32–35°F. The 29.1% cube, a high-end test, held 36–40°F the whole time, even after it had fully melted at 5 hours 12 minutes. The control cube started losing shape at the first hourly check.
Test #2: fiber type, on video
Two enclosed trays, one with shredded toilet paper and one with shredded cotton balls, about 29% fiber by volume each, on an open rack in a room near 70°F. The two trays stayed within ±3°F of each other throughout. Both stayed in the freezing range for up to 45 minutes and above 32°F for the rest of the run, with two identifiable ranges, 34–39°F and 43–47.5°F. The run was stopped at 4 hours 10 minutes, with the highest reading at 50°F.
Replicate it yourself
Any long fiber works, including cotton balls, recycled newspaper and toilet paper, but longer fiber gives better results. Mix the fiber evenly through the water before freezing; uneven mixing was the main cause of early failures.
