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Darn Tough RFL Over-the-Calf Ultra-light Review

RFL Over-the-Calf Ultra-Light
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Price:  $24 List | $23.00 at REI
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Pros:  Wick moisture well, warm when wet, lifetime guarantee, stylie
Cons:  Not a cozy feel, constricting for larger volume feet
Manufacturer:   Darn Tough
By Andrew Soleman ⋅ Review Editor  ⋅  Oct 6, 2017
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#3 of 5
  • Comfort - 30% 7
  • Warmth - 20% 9
  • Drying Speed - 20% 9
  • Fit - 20% 9
  • Durability - 10% 7

Our Verdict

The Darn Tough RFL Over-the-Calf Ultra-light is made to perform in a whole range of conditions: Sun or sleet, corduroy or powder, these socks are ready to take it on. For skiers who demand a tight fitting boot and cannot compromise on thickness in their ski socks, Darn Tough Over-the-Calf Ultra-light ski sock is the answer. We found the Darn Tough to be snug if even tight fitting, but thought it was lacking in the cozy feeling we got from socks like the SmartWool PhD Ski Medium.

Product Updated Since Testing
The RFL Over-the-Calf Ultra-Light, pictured above, is the updated prototype of the Over-the-Calf Ultra-Light. To learn about what's been tinkered with, keep reading.

That being said, when high output is required, the Darn Tough is vey efficient at staying warm, even when things became wet. If you're looking for a high performance quiver sock, not just something that makes you feel good, the Darn Tough Over-the-Calf Ultralight is a great choice.

Compare to Similar Products

Our Analysis and Test Results

The Latest RFL Over-the-Calf Ultra-Light vs. the Original

One of the drawbacks of the original Over-the-Calf Ultra-Light socks that we tested was the fact that they didn't have that nice cozy feel. The new version of this sock, the RFL Over-the-Calf Ultra-Light, is made with Darn Tough's "light and lux" wool, which according to one of their reps is "really soft, but just as tough". The acronym RFL added to the front of the title stands for "Run Fast Light," referring to the ultralight status of this product. The RFL socks are available in either black or red and cost one dollar more than their predecessor.

See the two versions below, with the latest prototype in Race Red on the left, and the sock we reviewed on the right.
RFL Over-the-Calf Ultra-Light
Darn Tough Over-The-Calf Ultralight

Here's a summary of the updates:
  • Materials - The RFL's newly features Darn Tough's "light and lux" wool which is a blend of 46% Merino Wool, 50% Nylon and 4% Lycra® Spandex (compared with 64% merino 33% nylon 3% lycra in the previous model).
  • Updated Colors — The new product is no longer made in the color or style that we originally tested. It's produced in Race Red and Black.
  • Cost Increase - The RFL costs $24, which is a dollar more than the previous model.

We haven't got around to putting these updated socks to the test, so the review below refers to the original Over-the-Calf Ultra-Lights.

Hands-On Review of the Original Over-the-Calf Ultra-Light

Tested up against the best ski socks on the market, the Darn Tough Over-the-Calf Ultralight created its own demand. With the highest warmth-to-weight ratio and a lifetime guarantee, these socks make a great choice for anyone who is of the notion that the thinner the sock, the better.

The Darn Tough Over-the-Calf Ultralight keeping things warm and dry deep into the afternoon  when we just could not get enough!!!!!!
The Darn Tough Over-the-Calf Ultralight keeping things warm and dry deep into the afternoon, when we just could not get enough!!!!!!


If you're buying socks for their cozy factor, these socks are not for you. Comfort in these socks comes from a lack of padding to allow you foot to sneak into performance fitting boots. Compared to the all other socks tested, they feel very thin. Some testers found these socks, like the Icebreaker, to be constricting around the foot, which resulted in cold feet.

Darn Tough Over-the-Calf Ultralight  the tallest and thinnest socks in our test.
Darn Tough Over-the-Calf Ultralight, the tallest and thinnest socks in our test.


The Darn Tough Over-the-Calf Ultralight is the warmest sock we tested for its weight. Despite the thin construction of these socks, they are very warm even when things get wet. Though these socks do perform well, they are not warm in the sense of cozy, and if that is of importance, the SmartWool PhD Ski Medium would make a better choice.

Wicking Ability & Drying Speed

Wicking moisture is what these socks do best. They are built with a high concentration of merino wool, and they compare similarly to the PhD in their performance. If this is the single most important factor in your decision making, the Icebreaker Ski+ Light is the best sock for you.

Ski Boot Fit

The Darn Tough Ultralight is set apart from the field in this category. With no padding in the foot and very little on the shin, this sock is made for a specific skier. While the SmartWool PhD will be better for a more loose and comfortable ski boot, the Darn Tough is ready to fit into the tightest ski boots out there.

The Icebreaker Ski+ Lite (left) compared with the taller and thinner Darn Tough Over-the-Calf Ultralight (right). The Icebreaker model wins for best wicking capability.
The Icebreaker Ski+ Lite (left) compared with the taller and thinner Darn Tough Over-the-Calf Ultralight (right). The Icebreaker model wins for best wicking capability.


Despite the thin nature of these socks, we were surprised at how quickly these socks began to deteriorate. We found them to get stiff under the balls of the foot after a single use, and could not get them to soften up after washing. Look to the SmartWool PhD if durability cannot be compromised.

Best Applications

These socks are made to perform. We found them to be best used as a quiver sock, when compromises in fit and performance cannot be made. Use this thin sock when you break out your performance boots, and wear a thicker, more plush sock on a casual day in looser boots.


At $24, these socks are not cheap. However, for skiers who demand that quiver sock, this is a great option, and with a lifetime guarantee you can continue to return socks that fail to meet your satisfaction.


Though there are many better options for the everyday skier, this sock is made for someone who knows exactly what they want. Darn Tough has delivered a quality product, and continues to maintain its position in the high end sock world.

Andrew Soleman