What is ArClo?
A tested number for how warm a boot really is.
ArClo is how Alaska Gear Company rates the warmth of our boots: no guesswork, just hard data from one of the nation’s most advanced protective-gear testing labs. We evaluate our lab results into temperatures you can plan around, with the same lab, the same test, and the same method for every boot.
higher ArClo = Warmer Boot
Clo is a standard way to measure how much warmth something traps. One clo keeps a person comfortable, sitting still, in a 70°F room. The higher the number, the more heat it holds in.
0
Nothing on at all.
0.04
Just underwear.
0.35
A thick sweater.
0.70
A winter coat.
1.5–3.0+
Gear made for extreme cold.
A boot is measured on a foot, not a whole body, so treat this scale as a guide, not a head-to-head with your coat.
We don't guess. We test.
Here's what happens when one of our boots goes to the lab.
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Meet the test foot
The lab uses a foot built to act like yours. It has nine sections, each with its own heater and temperature sensor, and it's designed to simulate heat and sweat.
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Put the boot on
The boot goes on the test foot with our Alaska sock, a merino-wool blend, just like you'd wear it.
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Chill the room
The foot is held at 95°F, about the temperature of your skin. The chamber is 41°F and humid, with a light breeze blowing across the toes.
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Measure the heat
The lab tracks how much heat the foot loses through the boot. The less heat that escapes, the better the boot holds in warmth.
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Repeat three times
Each boot is tested three times and the results are averaged into one clo number.
VBX Keeps Insolation Dry
Because each of the nine sections has its own sensor, we can see exactly where a boot is warmest and where it's thinnest, with no cold spot hiding behind an average.
ArCLO Temperature Rating
Comfort: wear it all day and stay comfortable. Capable: good for real work or time outside. Max: the coldest it's built for, for short stretches, not all day.
arclo, explained.
What does "ArClo" mean?
ArClo is our warmth rating. It's built on the clo, a standard unit for how much heat something holds in. We test every boot the same way and show you the result.
What's the difference between Comfort, Capable, and Max?
Comfort is all-day warm. Capable is warm enough to work or spend time outside. Max is the coldest the boot is built for, so think minutes, not hours.
Who does the testing?
A university lab: North Carolina State University's Wilson College of Textiles. They use a heated test foot and a published standard, ASTM F3426, to measure how much heat each boot holds in.
Does the lab pick the temperature ratings?
No. The lab measures insulation. We turn that into Comfort, Capable, and Max temperatures. Lab results can't predict exactly how any one person will feel, which is why we give you a range.
How is ArClo different from a generic "temperature rating"?
Many cold-weather products print a temperature with no testing behind it. ArClo starts with a measurement from a lab, using the same method on every boot.
Does it matter what else I'm wearing?
Yes. Warmth adds up, so socks, layers, and staying active all count. Our tests use the Alaska sock, so wearing it gets you closest to the tested result.
Is a higher ArClo number always better?
A higher number means the boot holds in more heat, but a warmer boot is also heavier and bulkier. Pick the one that matches how cold it gets where you're headed.
Lab results show how much heat a boot holds in under controlled conditions. How warm you feel also depends on activity, moisture, wind, and what else you're wearing. ArClo ratings reflect testing with the AKGC wool sock. ArClo is a guide, not a guarantee against frostbite or cold injury.
