Designed in Japan
Shop NowSo comfortable and breathable
"I procrastinated “splurging”on these for the longest time and they really are worth it. Great for traveling and working out, and they’re sustainably made."
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$35.00
This item's price has been updated recently to ensure you get the best value.
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$35.00
This item's price has been updated recently to ensure you get the best value.
Last priced at -
Soft and stretchy merino wool underwear with a modern slim fit, the Siren Bikini features our corespun fabric that’s incredibly soft and durable.
Good for:

83% Merino Wool/ 12% Nylon/ 5% Elastane, Exclusive of decoration
Machine wash cold gentle cycle. Wash with like colors. Do not use softeners. Do not bleach. Do not tumble dry. Line dry in shade. Cool iron. Do not iron print. Do not iron decoration. Do not dry clean.
Fit
Slim
Overall rating: 4.642738 / 5 from 599 reviews.
The Women's Merino 150 Siren Bikini is praised for its soft, breathable, and durable fabric. Customers appreciate its good quality and stylish appearance. However, opinions on sizing and coverage vary among users.
Review topics: ["fit","size","weather","coverage","quality","material","looks","colour","feel","shape","underwear","undies","buy","cut","stay","wool","bottom","side","space","breathability","fan","waistband","briefs"].
"I procrastinated “splurging”on these for the longest time and they really are worth it. Great for traveling and working out, and they’re sustainably made."
— Al (5/5)
"These are awful. I have probably a dozen pairs of Icebreaker bikini & hipkini briefs. I love their breathability, but have always been frustrated by how quickly they develop holes. This is the worst pair I've had by far (passion color, 150 merino). They developed a number of holes on the first wash."
— Lina H. (1/5)
"This is my favourite underwear. I love that the two pack offers them at a bit of a lower price."
— Ashley (5/5)
"I purchased the Women’s Merino 150 Siren Bikini for my wife, and she absolutely loves them. The merino wool is incredibly soft and breathable—nothing like traditional wool that can feel itchy. They’re lightweight, comfortable, and perfect for everyday wear, whether at home, traveling, or layering for outdoor adventures. She especially appreciates how well they regulate temperature and wick moisture, keeping things fresh throughout the day. The fit is flattering and stays in place without digging in or bunching up. They also wash and wear really well, maintaining their shape and softness over time. Icebreaker has really mastered comfort and practicality with this design. Highly recommended for anyone looking for premium-quality, natural-fiber underwear that feels as good as it performs."
— Joshua N. (5/5)
"Most comfortable underwear ever."
— Ashley (5/5)
"If you haven't slipped into something this comfortable yet, you are missing out. These are a game changer in life and on the adventure trail."
— Julia C. (5/5)
"I love these. They are so breathable and comfortable. I've owned several pairs for over 2 years and they are still like brand new. Machine wash and hang to dry (although i have dried them a few times without skinage, piling or wear). I wear size M and size 30 jeans."
— Nicole F. (5/5)
"They fit well and are comfortable."
— Fion T. (5/5)
"My favorite briefs!"
— Ingrid K. (5/5)
"Only underwear I use"
— Julie M. (5/5)
Find the size that fits you best based on people just like you.

Use the chart below to determine your size. If you’re between two sizes, order the smaller size for a tighter fit or the larger size for a looser fit. If your measurements for chest and waist correspond to two different sizes, order the size indicated by your chest measurement for tops and your hip measurement for pants.
Sizing charts:
| XS | S | M | L | XL | XXL | |
|---|---|---|---|---|---|---|
| Waist | 24-26 | 26-28 | 28-30.5 | 30.5-33 | 33-36 | 36-40 |
| Hip | 33.5-35.5 | 35.5-38 | 38-40 | 40-42.5 | 42.5-45 | 45-48.5 |
| XS | S | M | L | XL | XXL | |
|---|---|---|---|---|---|---|
| Waist | 61-66 | 66-71 | 71-77 | 77-84 | 84-91 | 91-101 |
| Hip | 84-90 | 90-96 | 96-102 | 102-108 | 108-114 | 114-123 |
*Looking for the inseam length? Please refer to the product page to find out.
Our three different fits - slim, regular, and relaxed - ensure that when worn together, layers move and breathe like a single garment.



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