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Smartwool PhD Ultra Light Review

A great choice for those who appreciate natural fibers, or who just want a durable and versatile running shirt
smartwool phd ultra light running shirt review
Credit: Smartwool
Price:  $70 List
Manufacturer:   Smartwool
By Andy Wellman ⋅ Senior Review Editor  ⋅  Apr 13, 2018

Our Verdict

Smartwool discontinued the PhD Ultra Light running shirt.
Durable and versatile
Fairly breathable and quick drying
Uses natural fibers
Still made of almost 50% synthetic fiber
Not as soft as others
The Smartwool PhD Ultra Light is unique because it is made of a blend of merino wool and polyester fibers, rather than being made only of polyester like most of the other shirts. It feels drastically different against the skin than the slippery and soft polyester, offering a far more natural feeling. Wool has other advantages as well, such as natural odor control, the ability to manage moisture in liquid or vapor forms, and great durability. The Ultra Light is an excellent choice for running or for other outdoor activities and offers runners an alternative to shirts that are purely synthetic.

Our Analysis and Test Results

The Smartwool PhD Ultra Light is made with two different types of fabric: a solidly woven but thin fabric on the front, tops of shoulders, and tops of sleeves, complemented by an airier perforated mesh on the back and undersides of the arms. Both of these fabrics are made of a blend of merino wool and polyester, in a ratio of roughly 56% merino and 44% polyester (although this varies slightly for the main fabric versus the mesh). This is the only shirt that we tested that includes natural fibers, but unfortunately for the hippies, still has a fair amount of synthetic material. The advantage of using wool is that it has interesting moisture management properties, is very durable and elastic, and has anti-odor and UPF protection naturally built in. On the other hand, it is not as smooth as 100% polyester and costs a bit more. Speaking of polyester, it is necessary to blend these fibers in because as we all know wool has the tendency to shrink mightily when washed, which the polyester protects against, and it also adds some silky softness to the feel.

Performance Comparison

smartwool phd ultra light running shirt review - the phd ultra light uses a blend of polyester and merino wool fibers...
The PhD Ultra Light uses a blend of polyester and merino wool fibers to offer awesome comfort and pretty solid breathability. Here running in the west fork area of the Zion backcountry.


When studying the comfort of a running shirt, we paid special attention to three factors: the fit, the fabric, and the seam sewing. There is no doubt that this is a comfortable shirt. The fit is athletic and slim, and this shirt hugs the body closely. We even felt the faintest hint of constriction in the sleeves and shoulders. There are a lot of seams on this shirt, and they are all sewn using the flatlock method that keeps protruding fabric to a minimum to reduce rubbing and chafing over time.

smartwool phd ultra light running shirt review - the fit of the  ultra light is fairly standard, meaning it isn't...
The fit of the Ultra Light is fairly standard, meaning it isn't large and baggy but doesn't literally hug the body.

The real story with this shirt is the fabric. According to Smartwool, merino wool has the curious attribute of having far thinner individual fibers than "regular" wool, reducing the ability for the ends to stay rigid and poke you, thereby reducing itching sensations. While we agree that this shirt feels nothing like a classical wool Christmas sweater, we also didn't think it feels quite as silky soft against the skin as, say, the Under Armour UA Tech. We have to admit that the feel of a specific type of fabric is certainly a personal preference, so we didn't penalize too much, but instead awarded 7 out of 10 for comfort.

smartwool phd ultra light running shirt review - in this photo you can see the slat locked seam stitching found...
In this photo you can see the slat locked seam stitching found throughout the Ultra Light, which we found to be comfortable and non-abrasive. The black material is lighter, airier mesh than the grey.


To aid in breathability, this shirt uses two different types of fabric, with the entire back and underarms being made of slightly thinner, more perforated fabric. While some might call this mesh, it is quite dense and hard to compare it to the super lightweight mesh prevalent in shirts such as The North Face Better Than Naked. Additional breathability comes from open vents across the back of the neck. Despite feeling thicker than other fabrics we tested, we couldn't deny the fact that it was fairly easy to force air through the mesh paneling, and so we gave it a relatively high score of 8 out of 10, the same score we gave to the Nike Dri-FIT Knit.

smartwool phd ultra light running shirt review - the preforated black mesh of the ultra light aids in breathability...
The preforated black mesh of the Ultra Light aids in breathability, as do the three open air vents, shown here, on the back of the neck.

Drying Speed

Wool can absorb up to 30% of its weight in water, allowing for moisture management either by mechanical diffusion or wicking. The open air vents and thin mesh on the back of the shirt also allow for direct air transfer, giving the Ultra Light perhaps the most versatile array of moisture management features. This shirt weighed 5.1 ounces, a fair amount more than the other top scorers for drying speed, and yet tied with the Brooks Distance and the Arc'teryx Motus Crew for third fastest drying time. There was a strong correlation throughout our drying speed test to fabric weight and drying speed, suggesting that heavier shirts had more fabric that could entrap liquid, and would, therefore, take longer to dry out. As a relatively heavy shirt but with a fairly fast drying time, the Ultra Light shattered that paradigm, giving solid credence to wool's ability to dry quickly. 8 out of 10 points.


Wool is known as a durable fabric, and while almost half of this shirt is made of mesh, we found the mesh to be thicker and more resilient than the mesh found on the Better Than Naked. In fact, we thought that this shirt ranked right up there with our Top Pick for Use as a Base Layer, the Arc'teryx Motus Crew, as the most versatile in this review. While it works great as a running shirt, we think this shirt also works great for wearing underneath warmth layers in the winter or wearing under a pack when hiking, climbing, or backpacking. We gave it 9 out of 10 points for versatility.

smartwool phd ultra light running shirt review - on a trail run in the beautiful and far less crowded high country of...
On a trail run in the beautiful and far less crowded high country of Zion wearing the Ultra Light. We thought this was a pretty versatile shirt, whether running or hiking, as well as for backpacking or winter activities.


We thought this shirt had a pretty good set of features, although it still didn't include the full complement for running shirts. It was the only shirt that didn't have a small sewn-in sweatband on the back of the neck, although this is a minor feature. While it does have three reflectors for greater nighttime visibility, these were all very small, and weren't found on all sides of the body like on the New Balance Ice 2.0. We loved how this shirt came with a UPF 30+ rating, and also that the merino wool has naturally odor resistant properties, without the need for chemical treatment.

smartwool phd ultra light running shirt review - while we loved how this shirt had natural odor protection and upf...
While we loved how this shirt had natural odor protection and UPF ratings due to the use of wool fibers, we wish it had a little more reflectivity than this small logo on the sleeve.

Best Applications

This is a great shirt for nearly any outdoor activity, whether that means running short distances or long, or instead hiking, biking, climbing, or backpacking. It seems especially well suited to those who want equal performance in both cool weather and hot.

smartwool phd ultra light running shirt review - the ultra light is a great choice for trail or road running, but is...
The Ultra Light is a great choice for trail or road running, but is also a good choice for hiking with a pack, or any number of other outdoor activities.


The Ultra Light retails for $70, making it the second most expensive shirt in this review. We believe that some of the cost can be attributed to using wool instead of cheaper synthetic fabrics. While we acknowledge that there were higher performing shirts available for a lower cost, we found this shirt to be versatile and durable, and think it presents a pretty solid value.

smartwool phd ultra light running shirt review - it sure is hard to beat vistas like this one, which is why we love...
It sure is hard to beat vistas like this one, which is why we love trail running. Here wearing the PhD Ultra Light.


The Smartwool PhD Ultra Light was the only shirt in this review to use a natural fiber. It blends merino wool with polyester in nearly equal amounts to gain the advantages of using both. We found it to be reasonably comfortable and to do a great job of managing moisture. We also appreciated the versatility it offered and enjoyed using it for many activities other than just running. While it was more expensive than most, we still think it is a shirt worth considering before making your purchase.

Andy Wellman
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