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Smartwool PhD Seamless Bikini Review

The PhD Seamless Bikini is an average product best used for cold weather
smartwool phd seamless bikini travel underwear women review
Credit: Smartwool
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Price:  $32 List
Manufacturer:   Smartwool
By Lauren DeLaunay ⋅ Senior Review Editor  ⋅  Apr 26, 2018

Our Verdict

Move over, cotton; wool is here to stay! A trusted source for all our base layers, we were intrigued by the notion of wool undergarments. We tried three very different wool products for this review, and the Smartwool PhD Seamless Bikini stood out as the thickest and most unique of the bunch. We liked how stretchy these undies were, but were a bit dismayed by its heavy weight and tight fit. We didn't like how constricting the leg openings felt, and with a slow drying time, we're not sure these undies are really to handle day after day of travel. While we had a hard time finding their appropriate niche, they did have many benefits over your standard cotton pair of skivvies.
Tight fit

Our Analysis and Test Results

With moderate scores across the board, the PhD Seamless Bikini didn't make it as an award winner, but we did find it useful in a variety of circumstances. We'd easily grab these undies as a compliment to our warmer base layers and for days when stability is key.

Performance Comparison

smartwool phd seamless bikini travel underwear women review - the phd seamless bikini gets its daily dose of vitamin d.
The PhD Seamless Bikini gets its daily dose of Vitamin D.
Credit: Lauren DeLaunay


While there are many ways underwear can affect performance, we know that comfort is key for any big adventure. For this metric, we became obsessed with materials. What is the product made of? Is it itchy? Stretchy? Is it thin or thick? Does it breathe? In general, we preferred thinner materials that had superior breathability without losing a luxurious feel.

Our testers were a bit disappointed with the Seamless. We found the wool to be itchier than the fabrics of its competitors, synthetic, and wool alike. While the Smartwool Merino 150 Bikini and Icebreaker Sprite Hot Pants both featured mega-smooth merino wool, the Seamless is considerably thicker and rougher.

smartwool phd seamless bikini travel underwear women review - stretchy and itchy in the phd seamless
Stretchy and itchy in the PhD Seamless
Credit: Lauren DeLaunay

Because the material is thicker, we struggled to find the same breathability that we found in ultralight models like the ExOfficio Give-N-Go Sport Mesh Hipkini and Patagonia Barely Hipster. These undies will keep you drier than your average cotton pair, but as far as overall all-day comfort is concerned, we just weren't impressed.


Closely connected to "comfort," we spent this category exploring each product's cut and construction. We evaluated stretchiness as well as the waist band, leg opening, and overall design to try and answer one essential question: will these underwear give us wedgies?

smartwool phd seamless bikini travel underwear women review - tight leg openings on the phd seamless
Tight leg openings on the PhD Seamless
Credit: Lauren DeLaunay

We didn't find any wedgies with the Seamless, but we did find a cut that was too tight, and we recommend sizing up or trying these on before you order your standard size. Equally stretchy throughout, with a similar design concept to the nearly seamless Under Armour UA Pure Stretch Hipster, the PhD Seamless isn't held back by a waistband or leg openings. These undies are surprisingly stretchy, but unfortunately not enough to make up for the tight sizing.

Drying Time

When we noticed how thick these undies were, our testers were immediately concerned with drying time. To get a more objective reading on breathability and water absorption, we conducted a formal drying time experiment. To do so, we gathered all the products in this review, soaked them in water, hand-wrung them, and then hung them on a clothesline to dry. Our suspicions were correct: the Seamless was one of the slowest models to air dry completely, similar in time to a conventional cotton pair of undies.

smartwool phd seamless bikini travel underwear women review - getting ready to towel-dry the phd seamless to test for water...
Getting ready to towel-dry the PhD Seamless to test for water absorption!
Credit: Lauren DeLaunay

When we're spending weeks or months on the road, it's helpful to be able to quickly rinse or hand-wash our undies so we can hop back on the trail right away. While some of the products we tested were dry in as little as 45 minutes, the Seamless took twice as long. After 90 minutes, we knew that drying time had been compromised by the thick construction, which set this contender back quite a bit in our final scores.


Once again, we knew we weren't getting the lightest product on the market with the PhD Seamless. Weighing in at 1.4 ounces, these undies were indeed one of the heavier models we tested. With products as light as .7 ounces, it's hard to ignore that these undies were up to twice as heavy as some of the competitors. Also, with such a plush fabric, the folding size of these undergarments was considerably larger than some of the thinner undies we tested.

We would like to point out, however, that we're negotiating portions of ounces here, not pounds. Our testers would argue that ounces themselves are hardly noticeable in one's backpack or suitcase, let alone portions of ounces. We encourage using weight and packability as a secondary metric when shopping for this reason.

smartwool phd seamless bikini travel underwear women review - the heavy phd seamless bikini compared to a black diamond neutrino...
The heavy PhD Seamless Bikini compared to a Black Diamond Neutrino carabiner
Credit: Lauren DeLaunay

Best Applications

While we've been quite focused on breathability and heat during this review, sometimes we venture into the cold as well. As a thicker, burlier pair of wool undies, the PhD Seamless could be a great addition to your winter layering system for that little bit of extra protection from the elements. While not the softest or comfiest product we tested, we would still recommend them over any cotton pair.


At $32, the PhD Seamless is on the steeper end of travel undies we tested. Because of their relative lack of breathability and slightly heavier weight, our testers just aren't quick to recommend shelling out so much dough for something we didn't love.


The Smartwool PhD Seamless stood up to some stiff competition in this review, making it difficult for us to award it one of our highest scores. While decently comfortable and reasonably stretchy, we were left yearning for the lightness and breathability of some of our favorite models.

Lauren DeLaunay
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