REASONS TO BUY
Lightweight
Comfortable
Both womens' and mens specific fit avaliable
Highly breathable
REASONS TO AVOID
Not durable
Slips down on the run
Foot slippage
Expensive
Smartwool PhD Run Ultra Light Micro Review
An expensive ultra-lightweight running sock with poor durability
Credit: Smartwool
RELATED: Best Running Socks of 2024
Our Verdict
The Smartwool PhD Micro Elite is a lightweight running sock composed of merino wool and nylon material. It offers no additional comfort features and provides great breathability on the run. While we wanted to love this sock (as we love most things Smartwool), we couldn't help but be disappointed. The fit of this sock is on the smaller side and changed after washing (with the correct directions). It's not nearly as durable as a running sock should be, showing the potential to bust out after just 30 miles of testing. More importantly, on the run, the back of the sock rolls down, causing annoying stops along the way for some of our testers. In conclusion, these are not a favorite.
Editor's Note: This review was updated on November 25, 2022, to note a name change and some material changes to this sock.
Compare to Similar Products
 This Product
Smartwool PhD Run Ultra Light Micro | |||||
|---|---|---|---|---|---|
| Awards |  Best Overall Running Sock |  Best Toe Sock | Most Comfortable Cushioning | Best for Wicking & Breathability | |
| Price | $17.00 at Backcountry Compare at 3 sellers | $20.00 at Amazon Compare at 2 sellers | $16.00 at REI Compare at 4 sellers | $20.00 at REI Compare at 3 sellers | $16.99 at Backcountry Compare at 2 sellers |
Overall Score  |
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| Star Rating | |||||
| Bottom Line | An ultralight running sock with good breathability but poor durability | An excellent all-around awesome contender that's built for long days on the trail or road | If you love to spread your toe, this toe-sock is our favorite for its excellent cushioning, comfort, and moisture management | An all-around performer that wicks well and offers extreme comfort, although it's not the most breathable | This sock offers the best wicking and breathability for those in need of dry feet all day long |
| Rating Categories | Smartwool PhD Run U... | Balega Blister Resi... | Injinji Trail Midwe... | Balega Silver No Show | Swiftwick Aspire Zero |
| Comfort (25%) | |||||
| Fit (25%) | |||||
| Wicking & Breathability (25%) | |||||
| Slip Prevention (15%) | |||||
| Durability (10%) | |||||
| Specs | Smartwool PhD Run U... | Balega Blister Resi... | Injinji Trail Midwe... | Balega Silver No Show | Swiftwick Aspire Zero |
| Material | 48% Merino Wool, 48% Nylon, 4% Elastane | 32% Drynamix Polyester, 32% Polyamide, 30% Mohair, 4% Microfiber, 2% Elastane | 39% Coolmax Polyester, 58% Nylon, 3% Lycra | 75% Drynamix Polyester, 23% Nylon, 2% Elastane | 55% Nylon, 40% Olefin, 5% Spandex |
| Ankle Cut | Micro | Quarter Length | Quarter Length | No Show Tab | No Show |
| Cushioning Level | None | Heavy | Heavy | Heavy | None |
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Our Analysis and Test Results
Product Update Note — November 2022
Smartwool no longer makes the PhD line of socks. This sock is now called the Run Zero Cushion Low and has a slightly different material makeup, with 2% more wool and 2% less nylon than before. The two versions are compared above, with the sock we tested shown on the left and the updated sock on the right.
Smartwool no longer makes the PhD line of socks. This sock is now called the Run Zero Cushion Low and has a slightly different material makeup, with 2% more wool and 2% less nylon than before. The two versions are compared above, with the sock we tested shown on the left and the updated sock on the right.
A lightweight merino-wool synthetic sock that is totally barebones. While we wanted to love the Smartwool PhD Micro Elite it simply does not measure up to other running socks out there. It's nice and breathable but lacks functionality while running with questionable durability.
Performance Comparison
Running it out on a hot day in the San Juan mountains.
Credit: Joanne Maczyk
Comfort
The Smartwool PhD Micro Elite is a lightweight no-frills option that lacks any major cushioning. It's best for those that don't need plush materials or extra protection underfoot. Constructed of an even amount of Nylon to Merino Wool, it is comfortable to wear on the trail. When feeling the fabric with your fingers, it's a little scratchier than most. However, on the roads and trails, it feels good to wear. We do enjoy the little bit of cushioning at the tips of the toes that adds a little protection.
Here we see next to no cushioning in the forefoot (similar to the heel). The material is soft against the skin, but the thin construction offers less comfort then thicker options. The good news is this sock does come with a more cushioned option.
Credit: Amber King
Fit
In general, the fit feels a little bit small out of the package, but once you get the right size, it does okay. The collar has a thin elastic band, that we wish, was a little beefier. The tab on the back protects the Achilles heel, but is a little shallow and didn't cover up all the way against some shoes that have a higher collar. During a few runs, we had to keep stopping to pull this sock up as it slid down the shoe. This would easily be fixed by designing the sock with a longer Achilles section in the back and a more elastic band.
Here we stop to adjust the Smartwool PhD Elite on a hot, sweaty day. This sock is slippery and somewhat small, making it slip down the foot.
Credit: Jo Marczyk
As we mentioned before, there is no additional cushioning in either the toes, forefoot, or heel. The elastic band around the arch of the foot keeps the sock in place, but doesn't offer a huge amount of compression, as we experienced with the Feetures Merino 10, a Top Pick for Comfort. Overall, the fit is okay, but some of our testers experienced it sliding down the foot when charging hard on flats.
The no-show tab is a little small and has a hard time protecting with shoes with a higher back.
Credit: Amber King
During our testing, we focussed on the women's running sock, but a men's version of this sock is available as well. The women's sock features a more narrow profile, thinner heel, and a smaller fit. If you're a woman with a wider foot, you might want to opt for the men's version.
Wicking & Breathability
It's thinner construction offers great moisture management. The sock is thinnest under the arch and throughout the top of the foot, offering great ventilation. While the stitching is tight, the threads are able to effectively wick away moisture from the foot. This is a great option for running in the Summer, Fall, and Spring.
The fabric is tightly knit and offers good wicking and breathing capabilities.
Credit: Amber King
Slip Prevention
Like most thinner socks, the Smartwool PhD Micro doesn't do much to prevent slippage. The merino wool-nylon fabric is slick and smooth and doesn't really stick well to the insole of a shoe. Since toe bump (on the downhill) can become an issue with these slippery contenders, we'd recommend a tighter fitting shoe if this is a concern. That said, there were no blister issues as a result of this slippage.
The tighter knit fabric means that this sock slips and slides in looser shoes or those with insoles that aren't super slippery.
Credit: Amber King
Durability
While the Ph.D. material used in Smartwool's sock is pretty durable in comparison to the rest of their fabrics, this still showed quite a bit of wear and tear after just the first use. The fabric pilled after the first wash (even with the correct washing directions). While this isn't a huge concern as it doesn't affect performance drastically, potential holes are.
A look at the forefoot that is almost worn through after just 30 miles on the trail.
Credit: Amber King
After 30 miles, we note an area where the big toe touches the top of the fabric. Here, we noticed the beginnings of a small hole. Under the sock, in high use areas, we note compression of the already thin material and stitching seriously wearing down. Also, after washing, it did shrink. Overall, we aren't super impressed with the durability and think there are more durable products out there to be considered with similar make-up.
Here we see where our big toe pushes into the fabric, forming a hole. Unfortunately, this is the same place a hole was punched through with another pair of the same socks, owned by the primary tester. Unfortunately, this is not the most durable sock. Though, the more cushioned version offers better durability.
Credit: Amber King
Value
While Smartwool has many great products, we aren't impressed by the performance and value of this particular product. There are higher-value options, with better construction and warranties.
Running on hot days is a wonderful application for this super ultralightweight sock.
Credit: Amber King
Conclusion
Smartwool has amazing products that are typically comfortable and great for all-around use. To be honest, we aren't especially impressed with the Smartwool PhD Micro Elite. While it is fairly comfortable for a lightweight sock, the fit is on the smaller side, it rides down on the run, and durability is questionable. If you're a hardcore Smartwool fan and have tried these socks, and they work, we are more then happy for you! However, we also believe there are better running sock options out there for the price.
—
Amber King
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