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Icebreaker Siren Bikini Review

This is a comfortable, lightweight, yet expensive wool base layer
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Price:  $35 List | $22.75 at Backcountry
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Pros:  Lightweight, quick-drying, merino wool
Cons:  Less practical fit, expensive
Manufacturer:   Icebreaker
By Lauren DeLaunay ⋅ Senior Review Editor  ⋅  Mar 10, 2020
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#6 of 9
  • Comfort - 35% 7
  • Fit - 30% 6
  • Drying Time - 25% 8
  • Packability - 10% 9

Our Verdict

The Icebreaker Siren Bikini is a cute garment great for a wide array of activities. With a mostly wool construction, it's naturally odor-free and soft, while the small percentage of Lycra adds a surprising amount of stretch. Our testing team found the bikini cut to be visually flattering and comfortable, but it definitely has less coverage than other bikini models we tried. While not the very fastest, it has an impressively quick trying time, and at just 0.7 ounces, it's one of the lightest models we tested, taking up virtually no space in our suitcase. After weeks of travel, we came to appreciate this wool piece even if it didn't make the cut for winning an award.

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Our Analysis and Test Results

The Siren is a simple, effective piece of travel underwear that is comfortable, quick-drying, and breathable, even if it isn't the top scorer in any single category. Out of all the products in this review, just under half are predominantly wool. Compared to the others in its class, the Siren is nearly on par for comfort, packability, and drying time; our main problem with it is the cut. While cute, we find the fit to be a little too tight without enough coverage for effortless activewear.

Performance Comparison

The Icebreaker Siren drying quickly in the Patagonian breeze
The Icebreaker Siren drying quickly in the Patagonian breeze


Compared to all the things we test here at OutdoorGearLab, underwear is a pretty personal one. We all like different fits and cuts, but our testing team worked hard to describe certain characteristics that would help all buyers make the most informed decisions. "Comfort," as we've defined it, refers to each product's next-to-skin feel, material thickness, and breathability.

The Siren Bikini is comfortable, but it didn't blow us away. Compared to many of its synthetic counterparts, we find the material to be not nearly as smooth and silky. With 83% merino wool, 12% nylon, and 5% Lycra, this isn't itchy like you might expect from wool, but it also doesn't have the luxurious feel of some other products we tested. That being said, if wool is your jam, this is one of our favorite pairs.

The austral summer sun illuminates the soft  stretchy wool of the Icebreaker Siren.
The austral summer sun illuminates the soft, stretchy wool of the Icebreaker Siren.

Our team enjoyed the thin material of the Siren, which led to great breathability and a decent feeling of wearing nothing at all. We like the thin waistband made of soft, simple nylon, but the leg openings are another story. The stitching on the leg holes seems more raised than others, and this is one of our least favorite parts of this product, though not a complete deal-breaker.


Fit, while closely linked to comfort, deserves its own category, and we'll tell you why. We realized pretty quickly during this testing process that there is one key question we could use to steer our scoring: how much does each pair of undies make it feel like wearing nothing at all? No one wants to spend energy while traveling fussing over underwear, so we identified the following traits to help us guide the "fit" section of this review: shape and cut, stretch, stability, and seams.

The Siren that we tested is in a "bikini" cut, though it is sold in a thong version as well. Our initial impression of this garment was that it offers much less coverage than we typically want when engaging in active or rigorous outings. Compared to other models in our review, the Siren is quite narrow with a lower rise. This might appeal to some buyers who are looking for something a bit more stylish, but as a performance piece of activewear, we think this detracts from its overall feel.

The Siren has much less coverage than other undies we tried  which wasn't our favorite for active outings.
The Siren has much less coverage than other undies we tried, which wasn't our favorite for active outings.

One great thing about the Siren is the stretch. We are really impressed by the elasticity, and we never felt held back by its fabric. Another thing we approved of is its "stability," — our nice way of saying that we never got any wedgies while wearing this product. The leg openings might be a bit tight, but forced to choose between a little bit snug or constant wedgies, we'd definitely choose snug.

Drying Time

Drying time is a pretty simple concept in underwear testing, but each product's score tells us two things: how dry will I stay when sweating, and how quickly will my clothing air dry? For this test category, we hung all the products on clotheslines after washing and soaking completely, and we also recorded our experiences hiking in hot, humid places.

The Siren does well here, and while it isn't the single fastest, it was nearly as close as some of the thinner synthetic models we tested. Hanging on a line to dry in southern Chile, we were impressed that with just a few hours, we could easily wash these undies, dry them, and get right back to the action.

Washing laundry in Cochamo would be easier if all our clothes dried as fast as the Icebreaker Siren!
Washing laundry in Cochamo would be easier if all our clothes dried as fast as the Icebreaker Siren!

One thing we noticed, both while washing and while sweating, is that the wool material of the Siren appears to fend off moisture more easily than other materials. While some synthetic products both soak up water and dry out quickly, the wool seems to fight off moisture. While this doesn't apply to washing, it does apply to hiking, running, and traveling in hot, humid environments.


Short and sweet, this category is about as simple as it gets. We want to know how much room each product takes up in our pack by both measuring its weight and evaluating its three-dimensional space.

Weighing the Icebreaker Siren to get an accurate read on packability
Weighing the Icebreaker Siren to get an accurate read on packability

As one of the lightest products in this review, the Siren takes up practically no room at all. We loved having this super-light garment (just 0.7 ounces!) with us on long backpacking trips, and as people who are routinely pushing the limits of airline baggage, our suitcases thanked us too.


As a wool product, the Siren Bikini is one of the most expensive products we tested for this review. While we do feel that it might be a good option for a shopper intent on wool who wants something with a more stylish cut, there are synthetic models out there are more than half the price and wool options that scored higher in our review.


The Siren Bikini left us a bit perplexed. We like it, but do we like it enough to justify the price? The shape is cute, but is it the most practical? At the end of our testing period, we decided that while this product may appeal to many buyers for its lightweight design and quick drying time, there are other garments in this review with higher overall scores that might be better for you.

The Icebreaker Siren was a great addition to our backcountry adventure thanks to its quick drying time and soft material.
The Icebreaker Siren was a great addition to our backcountry adventure thanks to its quick drying time and soft material.

Lauren DeLaunay