Merino Wool's Less-Discussed Benefit: It Makes Fire Resistant Socks

Welder working on pipe, sparks flying, good thing he's wearing fire resistant socks from darn tough

When you consider the benefits of Merino Wool, the fact that it makes great fire resistant socks probably isn’t one that you’ve put much thought into.

Most people don’t need to verify that their socks are “Safe to Fly”or No Melt No Drip. But if you’re a wildland firefighter or flying with the Air Force, this less-discussed benefit of Merino Wool might rank high on your list of considerations when choosing socks that are comfortable, durable, protective, and approved for use under military uniforms and protective equipment.

Here’s why Merino Wool is the best choice for naturally fire resistant socks: 

  1. Merino Wool is difficult to ignite 
  2. It will self-extinguish in the absence of a flame
  3. It may smolder, but burning wool will not melt, drip or stick
  4. Wool fibers resist static buildup so they won’t cling or spark

Merino Wool Is Naturally Fire Resistant - Let's Discuss

Man seated by fire wearing darn tough wools socks

If you were thinking that your Merino Wool socks could double as firestarters in a pinch…think again. Merino can burn, but it makes poor tinder.

When compared to other natural fibers, like cotton or rayon, Merino Wool is the most difficult fiber to ignite, with the high ignition temperature of 1,058-1,112 degrees Fahrenheit. In order to burn, wool fibers need higher levels of oxygen than are available in the atmosphere and have a higher heat of combustion and ignition temperature than other natural fibers. These qualities make wool your best choice for next-to-skin fire resistant socks.

If Merino Wool is exposed to an open flame it will burn. However, once the flame source is removed, the wool will stop burning. Wool's cross-linked cell membrane structure enables it to self-extinguish and prevent the spread of flames to neighboring fibers. And burning wool will not melt, drip, or stick like synthetics are known to do. 

Man and woman pulling on wool socks and other warm clothing in the morning

In extreme heat (think wildland firefighting heat) fire resistant wool socks not only form an insulating layer that protects skin from flames but can also help maintain a more consistent temperature around the feet through thermoregulation. Don’t take our word for it though. Read what firefighters have to say about wearing Darn Tough Merino Wool socks on the job:

Best Firefighting Socks — Firefighter Reviews

The Best Socks for Firefighting

I fought wildland fire in these socks all summer last year and NOTHING CAN COMPARE. Every single one of my coworkers got horrible blisters from their boots but these socks totally saved me. Even though it was extremely hot in my work environment, these were able to keep my feet cool and protected, despite advertising for cool weather. If you need socks for professional use, I can not recommend these enough. In fact, they are so comfortable I now wear them with my nice boots when I go out on the off season. 11/10. - Dagny

Best Socks Ever!

For those that are working on their feet every day, you owe it to yourself to own a pair of these socks. As a firefighter I wear boots every day. On my off days I’m wearing boots. These socks will be in my feet before anything else! It took a full two years to wear through a couple pairs of these socks. The warranty process was as easy as can be. If you give these socks a chance, you’ll never need to buy another! - Cody

'Safe to Fly' Socks for the U.S. Air Force

A pair of Air Force ocp socks hanging in front of a helicopter

Civilians may take fire resistant socks for granted, but in the Air Force socks are serious business. In fact, the word sock comes up 53 times in the 160 page document detailing standards of dress and personal appearance for Air Force personnel.

Socks for Air Force service members must be wool or cotton, materials must be Berry compliant, only approved colors may be worn, and only those items that have passed the Safe to Fly Air Force test for Flame Resistance and No Melt No Drip can be worn during flying operations.

Darn Tough Tactical wool socks meet the procurement and technical requirements of Berry Compliance, and are available in the regulation Operational Camouflage Pattern (OCP) sock colors of black, green, coyote brown, and tan. They can be worn in military boots with combat uniforms, service uniforms, dress uniforms, and physical training (PT) uniforms.

T4021 fire resistant socks for military boots hanging over a railing in approved ocp colors

The T4021 and T4033 Boot and T4050 Over-the-Calf styles have specifically received the US Air Force Safe to Fly Product Certification and are authorized for wear with Air Force flight duty uniforms, fuel handler coveralls, and flame resistant advanced combat uniforms.

Since cotton is listed as an approved fiber for Air Force socks, it seems important to mention that given a choice between cotton or wool socks for comfort, durability, and protection — wool wins hands down.

Just read Why You Shouldn't Wear Cotton Socks for the 411 on how wool socks are superior for foot health and long days spent in military combat boots. Then check out what these members of the U.S. Air Force have to say:

Wool Is Your Best Friend — Air Force Reviews

After 2 Years of Daily Wear...

These socks are absolutely the best value in clothing you can find. I work the flight line at an Air Force base in Tucson, Arizona. These socks wick sweat like no other. I own 15 pair due to a generous uniform allowance. I might have sold 30 more pair to co-workers due to my recommendations and enthusiasm for the quality and performance of these socks. I also use them for cycling and running. Strongest recommendation. Great in the heat and the cold. Wool is your best friend. - Nathan

Great Socks!!

I first bought 2 pairs of these for our son who is in the Air Force stationed in Germany for Christmas and he loved them!! So I decided to get 3 more pairs for him so he has enough for a full week of comfort. Thanks for making the fact that he is on his feet so much easier to deal with! - Karen

Great Comfort/Durability

These tactical Darn Tough socks are the best you can get that are within regs for the new Air Force and Army uniforms. The medium weight are not too hot for me in Hawaii, but in the Middle East or Florida/Arizona it might be too warm. I hope Darn Tough will make these in a lighter fabric in the future for hotter climates. I bought 6 pairs which should last me until the next uniform change, haha. - Jared

Merino Wool Resists Static Build Up

Work, about to put on boots, wearing static resistant merino wool socks

For anyone regularly working around a heat source, flames, or flammable substances, preventing sparks of any kind is an important fire safety precaution. Pairing static and fire resistant wool socks with protective fire retardant clothing and equipment improves comfort (they won’t cling), and and they will not throw sparks. 

So, how does Merino Wool’s static resistance work? It’s essentially a byproduct of wool fibers’ natural ability to thermoregulate, which is driven by its absorption and moisture wicking abilities.

When we talk about wool moisture management, the focus tends to be on how each Merino fiber can absorb up to 30% of its weight in water (read: sweat) without feeling wet to the touch, as it pulls the moisture away from skin and moves it toward the surface where it can evaporate. This process means wool can keep you drier while maintaining a more consistent and comfortable temperature next to skin.

The less-discussed benefit of wool’s ability to absorb moisture is that it prevents static electricity from building up, which means wool fabrics won’t cling or spark. 

Telephone lineman seated on back of track pulling on boots and wool fire resistant socks

FYI: To be fair, cotton fibers absorb water too (2700% of their fiber weight) - so they can resist sparking as well. What cotton can't do is manage moisture like wool, so it leaves you feeling wet and uncomfortable (and can even be dangerous in certain conditions).

Hot tip: Darn Tough has a collection of Merino Wool work socks that are designed with long hours spent wearing rugged, protective footwear in mind. 

TL;DR — Merino Wool Is Great for Firefighters & Air Force Approved

Are Merino Wool socks fire resistant? Yes, Merino Wool fibers are difficult to ignite, have limited ability to sustain a flame, and can self-extinguish.

Are Merino Wool fibers non-flammable? Yes, because Merino Wool fibers require more oxygen than is available in the atmosphere to ignite.

Can Merino Wool socks burn? If exposed directly to a flame, Merino Wool fibers will burn. However, once the flame is removed, the wool will self-extinguish.

Are Merino Wool socks good for firefighters? Yes, because Merino Wool is naturally flame resistant, self-extinguishing, and won’t melt or drip when exposed to extreme heat.

Is there an ideal wool weight for firefighter socks? The general rule is: more Merino fibers = more Merino benefits. If your feet sweat a lot during long hours in protective boots, a midweight wool sock can actually do more to keep feet comfortable and protected. 

Can wool socks help prevent blisters? Yes! Sweaty socks lead to blisters. Merino Wool socks absorb sweat and dry fast to keep feet comfortable and blister-free.

Are there ‘Safe to Fly’ certified Merino Wool socks? Three Darn Tough tactical sock styles (T4021T4033, and T4050) have passed the Safe to Fly Air Force test for Flame Resistance and No Melt No Drip.

Does Darn Tough have approved Air Force uniform socks? Darn Tough tactical socks are certified Berry Amendment Compliant with all yarns sourced in America, and the colors are compliant with most uniform requirements.

Are Merino Wool socks static resistant? Yes, the retention of moisture within Merino Wool fibers prevents a build-up of static electricity and associated sparking.