Making the Most Durable Socks

Ultrarunner seated pulling on well-worn darn tough socks, the most durable socks

At Darn Tough, we back every sock with our Unconditional Lifetime Guarantee: if our socks aren’t the most comfortable, durable, and best fitting socks, you can return them for another pair. Durability sits in the center of that promise.

But what makes Darn Tough socks so… tough? We won’t share the whole recipe (that’s confidential), but here are some of our tried-and-true ingredients that together make the world’s most durable socks. With three generations of knitting know-how under our belts, we know a thing or two. And the proof, well, it’s in the stitching.

Why Durability Matters

Before we get into the how, you might wonder why. Not why we have spent so many years developing durable socks – when you lifetime guarantee your socks, the business case for durability speaks for itself – but why promise durability at all? Especially for something as high wear as socks?

A few reasons:

The best socks are durable. You know that feeling when your toe punches through the front of your sock? Exactly. Best case scenario, you’re stuck at a dinner party debating leaving your shoes on. If you’re on the trail when that happens… yikes. Your first line of foot care failed you. Hikers, runners, construction workers, firefighters - they all depend on their socks. We want to make sock blowouts a distant memory.

The best socks are sustainable. A long-lasting sock is a sustainable sock. If one sock can do the job of ten, that’s nine pairs that aren’t adding waste to the environment. That’s also nine pairs you didn’t have to buy (we support financial sustainability, too). Every time we increase our socks’ lifespan, that math improves. We aren’t saying one Darn Tough sock = ten normal socks. Depending on what “normal sock” means to you, we might be well past that.

A promise to you, a challenge to us. We believe we’ve yet to produce our best sock. The best sock we can make is a more durable sock. Guaranteeing durability keeps us from complacency, from making super comfortable socks that only last a year. Every worn-out pair that comes back to us through warranty reminds us we can do better and shows us where improvements can be made. We believe they’re durable, so we guarantee them. We guarantee them, so we’re always making them more durable.

What Is Durability?

Feet wearing darn tough socks so covered in mud they've turned brown

Tough, long-lasting, reliable… you get the idea. Durability is a staying power, an ability to hold up for a long time under pressure or wear.

But there’s more to durability than longevity. A sock that lasts forever but isn’t comfortable, isn’t preventing blisters, and isn’t protecting your foot, isn’t durable in a way that’s useful. That’s why we also guarantee comfort and fit.

To pull those pieces together, a durable sock is a sock that has no holes and isn’t threadbare, while still maintaining comfort and fit wear after wear after wear.

How many wears? That varies. Some of that depends on you, on how the sock is cared for. But it’s not uncommon for our socks to last over a decade.

How to Make Durable Socks

Our socks are more durable today than they were a year ago (and they were durable then, too). So what makes our socks so durable?

Years of Experience, Testing, & Feedback

We’ve been making socks since the 1970s, and we’ve been guaranteeing them for life since 2004, longer than anybody. Our lifetime warranty doesn’t just get you a new pair of socks – it gets us your old pair.

Old Darn Tough Hiker Boot socks that came back through warranty

When you sent that old, worn-through pair of socks back to us, you gave us invaluable feedback. There’s no greater research lab than real life, and our warranty program acts as a robust testing program with an endless supply of data. And we’re not afraid to use it.

We’ve been collecting worn out socks and studying them to make improvements longer than anyone else. We have people here who can look at a pair of socks and say, yep, that’s a toenail hole. (Yes, we know who trims their toenails and who doesn’t.)

A warrantied pair of darn tough hiking socks, well-worn and giving us feedback

We also know how different activities wear and tear socks differently. That threadbare area over the Achilles? Hiking boot rub. We can (and did) fix that.

Processing all our warranty feedback, applying fixes, then processing those socks when they come through warranty – it’s a cycle of constant learning and improvement. After all these years, not only can we identify wear and tear patterns, but we also know how to fix them.

A pair of lifestyle socks we got back through warranty, with lots of everyday wear

High-Density Knit

You may have heard us mention high-density knitting before. It refers to the small needle, fine gauge knitting machines that we knit all our socks on. These machines have lots of needles that make teeny tiny stitches.

The inside of our knitting machine, showing all 168 needles knitting tiny stitches

To understand why that matters, picture chain mail (part of the armor you see in Lord of the Rings, Monty Python and the Holy Grail, etc.). Chain mail is thousands of tiny, interconnected metal links. Why tiny? Because the smaller the links are, the less likely a sword, arrow, or other medieval weapon can puncture it. Bigger isn’t always better, and when it comes to medieval baselayers and knit fabrics, having more of a small thing leads to increased durability.

To that end, our machines have 168 needles. Why 168? Why not 200, 300? We’ve learned 168 is the sweet spot. The stitches are tiny, but not so tight we can’t add other durability enhancements.

Different fibers, with different stitch types, mixed in the right amounts, have a stronger resistance to abrasion. This is where that confidential stuff comes in.

Top Secret stamped over a diagram of different sock fibers

We can’t tell you the exact formula, but the point is, we have this art form mastered. You want a stitch count high enough to be super durable but not so high you can’t beef it up. That’s why 168 needles.

Naturally Durable, Top-Quality Materials

To make the most durable chain mail, you want to have tiny links, and you want to make them out of an already naturally durable metal, something that won’t shatter on the first impact. The same is true for socks.

We start with Merino Wool, a naturally durable fiber. Merino fibers are made of interlocking protein molecules, allowing each individual fiber to stretch and recover without losing elasticity or breaking. This resilience on the fiber level leads to an extremely strong, robust yarn that, when turned into fabric, can hold up under years of use.

To capitalize on this natural endurance, we always use 100% Merino Wool yarns, never a blend. To Merino, we strategically add in top tier Nylon and Lycra Spandex yarns (assisting with durability and fit, respectively). Our quality team tests the tensile strength of these yarns when they arrive at our Mill, making sure they meet our strict quality standards.

Bring in the Reinforcements

Our warranty feedback helps us identify high-wear areas that are more likely to give out. Many of those areas vary based on activity. E.g., all socks are prone to see-through footbeds, but a work sock in steel toe boots might sprout a toe hole, while a hiking sock might wear through at the Achilles.

Based on years of activity-specific feedback, we reinforced our socks to perform for the activity they’re built for. Two reinforcement techniques are Nylon and cushion.

  • Nylon: this durable fiber acts like an exoskeleton, reinforcing the sock from the outside. We knit Nylon into the outside of socks in key high-wear zones to protect against abrasion, wear, and tear.
  • Cushion: this is how we create an endoskeleton, reinforcing the sock from the inside. Cushion is knit terry loops that add more material. More material takes longer to wear through, making cushioned areas more wear resistant.

To reiterate, we make these enhancements based on a sock’s intended use. We design our Hiking socks to hold up to the rigors of miles and miles of rough terrain. You can (people do) go hiking in our Lifestyle socks, and they’ll likely last a long time, longer than another casual sock would. But hiking isn’t what they were designed for, so yeah, you might put a hole in them 600 miles in. Flip side, if you wear our Hike socks around the house instead of on the trails, they might just last forever.

Abrasion Testing

The feedback we get from warranty is invaluable, but we don’t rely on only that. We also conduct our own internal and external testing to see if new techniques and socks can hold up.

The Martindale Abrasion Tester is how we check our work before sending it out to you for in-use testing. Essentially, this machine stretches the sock then rubs it with metal sandpaper. Nonstop, for hours. The Martindale makes it clear whether our work holds up or not.

The Right Fit

Darn Tough employee testing the stretch of a sock and taking notes

There’s a lot of reasons you want your sock to fit right, and we’ve discussed fit and what goes into making the best fitting socks at length elsewhere.

When it comes to durability, fit plays an important role. Constant chaffing and rubbing produces friction that wears away at your socks. If your sock doesn’t fit right, it’s going to slip, slide, and otherwise move around, causing friction. The better your sock fits, the less this will happen, and the longer it will last.

Durable Socks: Our Promise

A giant pile of darn tough socks, all different styles and colors, all incredibly durable

Feedback, materials, knit, fit, test, repeat. It’s a cycle we’ve repeated countless times, and based on your feedback, it’s paid off:

"I am a supervisor for a 6,000 sq. foot warehouse and average about 12,000 steps a day on dense concrete floors. You should know I blew through 3 pairs of work boots before I finally wore out a pair of Darn Tough socks. Keep up the good work guys!" — Bill G.
"These are the only socks I backpack with. I’ve done the Pacific Crest Trail, hundreds of miles through Europe, the Arizona Trail, etc., and these are the most durable quick drying, sweat wicking socks I’ve had. I’ve had to replace a few pairs over the years. Darn Tough has an easy online form you mail in with the socks. Within a week, I received my online credit which covered the complete cost to replace each pair. Within the next week, I was packing them for another backpacking trip!" — Tori B.
"I am a tractor mechanic, and spend 10-12 hours a day on my feet wearing steel toe boots. I would ruin normal boot socks after wearing them 10-15 times. I bought two pairs of these socks to start out. I have been wearing them 3 times a week for a month to see how they hold up. These socks are the most comfortable and durable I have ever worn. They feel the same as new, and show no signs of wear." — Jeremy H.
"I run about 30 miles a week and try to do a couple of half marathons a year. After trying a number of different socks, these are the most comfortable, most breathable, most durable, and hands down best running socks I have ever used. I cannot recommend these enough." — Ian R.
"I've been wearing Darn Tough socks everyday ever since I got my first pair for our Thru-hike attempt of the PCT. There was no turning back for me. Most comfortable and durable socks on and off the trail. My go-to present for Birthdays and Christmas as well." — Cyril B.
"I purchased six pairs of Darn Tough's tactical cushion socks over eight years ago for a deployment. My job consists of being on my feet at least 12 hours a day, six days a week, in a construction field with a ruck march here and there. Eight years later with the same six pairs of socks, walking, working, and hiking, the socks finally wore out. I would recommend Darn Tough's socks to anyone, no matter how much or how little you are on your feet." — Brandon G.
"My husband and I just got back from a backpacking trip— I did 30 miles and he did the entire foothills trail which is 77 miles! He wore the same pair of darn toughs the entire time. One pair to hike in and one time to sleep in. So did I and our friend who was with us wore the one pair his entire 77 miles. We all agree that these are seriously the best, most durable socks ever! EVER!!! We will not hike in another brand." — Lindsey J.

Durability, Guaranteed

“How do you guarantee your socks for life?”

We get that question a lot. Hopefully at this point, you have an idea why we can speak about our socks’ durability and guarantee it with such confidence.

A Darn Tough sock that's starting to wear out after miles on the trail.

Does that mean our socks never wear out? No. And there are steps you can take to make them last longer: proper washing and drying, choosing sock type based on footwear and primary activity, and low-stress folding techniques, to name a few.

But if you do manage to put a hole in our socks, our hat (shoes) goes off to you. We wear our socks, so we know how much work that takes. And we stand behind our guarantee. Go ahead and send those socks back to us – we’ll get you that replacement and take notes on how to make our next most durable socks. And you have a good story to go with them, we'd love to hear it.