Why not make all army uniforms out of Nomex? Poor moisture management. Not the best choice for troops running around sweating in the Middle East. And Nomex is expensive. And difficult to print with camouflage.
This is how it goes with protective textiles: Everything is a trade-off. Everything is a problem. Even the color. Darker colors reflect less heat; they absorb and transfer more of it to the skin. Auerbach goes across the lab to get a swatch of camouflage print cloth. She points to a black area. “You can see this has a pucker where it was absorbing more heat.”
“It has a what?” I heard her, but I need to hear her say pucka again. The fabulous Boston accent.
I would have guessed the military to be a fan of polyester: strong, cheap, doesn’t ignite. The problem is that it melts and, like wax and other melted items, it drips and sticks to nearby surfaces, thereby prolonging the contact time and worsening the burn. What you really don’t want to be wearing inside a burning army tank is polyester tights.?
To determine what degree of injury the heat would produce, Auerbach runs the reading from the sensor behind the cloth through a burn prediction model—in this case, one developed after World War II by original flame goddess Alice Stoll. Stoll did burn research for the Navy. To work out first-and second-degree burn models, she gamely volunteered the skin of her own forearm. You may excuse her for letting someone else help out with the third-degree burn curve. Anesthetized animals were recruited for this—rats, mostly, and pigs. Pig skin reflects and absorbs heat in a manner more like our own than that of any other commonly available animal. The pig as a species deserves a Purple Heart, or maybe Pink.
What Stoll learned: When flesh reaches 111 degrees Fahrenheit, it starts to burn. The Stoll burn prediction model is a sort of mathematical meat thermometer. The heat of the meat and how deeply into the skin that heat penetrates are the critical factors that determine the degree of the burn. A brief exposure to flame or high heat cooks, if anything, just the outer layer, creating a first-degree burn or, to continue our culinary analogy, lightly seared ahi tuna. A longer exposure to the same heat cooks the inner layers, too. Now you have a second-or third-degree burn, or a medium-rare steak.
Even without a flame, clothing can catch fire. The auto-ignition temperature for cotton, for instance, is around 700 degrees Fahrenheit. Exposure time is key. The heat pulse from a nuclear blast is extremely hot, but it’s traveling at the speed of light. Might it pass too quickly to ignite a man’s uniform? Natick’s early precursor, Quartermaster Research and Development, actually looked into this.
Operation Upshot-Knothole was a series of eleven experimental nuclear detonations at the Nevada Proving Grounds in the 1950s. The Upshot-Knothole scientists were mainly interested in the blastworthiness of building materials and tanks and bomb shelters, but they agreed to let the uniform guys truck over some pigs. Anesthetized Chester White swine, 111 in total, were outfitted in specially designed animal “ensembles” sewn from different fabric combinations—some flame-resistant and some not—and secured at increasing intervals from the blast.
Flame-resistant cool-weather uniforms with a layer of wool outperformed a series of thinner flame-resistant hot-weather uniforms—whose developers had surely, by “hot weather,” not had in mind the extreme swelter of nuclear blast. The researchers marveled to note “a complete lack of any qualitative evidence of thermal injury to the fabric-protected skin of animals dead on recovery at the [1,850-foot] station.” I don’t wish to be an upshot-knothole, but who worries about burns on subjects close enough to a nuclear explosion that they are, as the report succinctly terms it, “blown apart”? Despite the clanging absurdity of the scenario, it was a memorable demonstration of the importance of exposure time. With the fast-traveling heat from a bomb—including a more survivable one like an IED—a few seconds of flame resistance can make all the difference.
The wool helped, too, because hair is naturally flame-resistant. Natick has, of late, been looking into a return to natural fibers like silk and wool. Not only is wool flame-resistant and nonmelting, it wicks moisture away from the body. Auerbach says she has seen some very nice, soft, flame-resistant cool-weather sheep’s wool underwear. The hairs have to be descaled so the wool isn’t itchy, and the garments need to be treated to keep them from shrinking, and both these processes add to the cost. As does the Berry Amendment, which gives preference to domestic suppliers of military gear. The Berry is additionally problematic in this case in that—despite the breathless, eager assurances of the American Sheep Farmer’s Industry—there may not be enough sheep in all of America to fill the bill.
So let’s say your new textile is comfortable and affordable. The flame resistance plays well with the insect-repellent treatment and the antimicrobial stink-proofing. Now what? Now you bring some over to the Textile Performance Testing Facility. You run it through the Nu-Martindale Abrasion and Pilling Tester to get a feel for how quickly the treatments will succumb to soldierly abuse. You subject it to a couple dozen wash and dry cycles. Laundering removes not only grime but also, bit by bit, the chemicals with which a cloth or fiber has been treated. When I visited the textile testing facility, a man named Steve was waiting for some pants to get through an accelerated wash. One wash in the Launder-Ometer equals five normal washes, he told me.
“That’s something,” I said.
“Yup.” He stuck out his lower lip in a contemplative way. “Steel balls bang against the fabric.”