New for Women
Shop NowFavorite icebreaker cut
"Love the neckline and cut of this top but definitely size up! So comfy, slightly stretchy, little more durable than some of the super lightweight fabrics."
Free standard shipping for orders above £40
Free returns
£69.99
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£69.99
Good for:

83% Merino wool/ 12% polyamide/ 5% elastane exclusive of decoration
Machine wash warm. Wash inside out with like colors. Do not use softener. Do not bleach. Do not tumble dry. Line dry in shade. Warm iron. Do not iron print and accessories. Do not dry clean.
Model measurements:
Height: 172cm / 5'8". Waist: 60cm / 23". Amande is wearing size S.
Key product measurements:
Inseam Length:62.5cm (Based on size M)
Slim Fit
A snug, close-to-body fit for low bulk layering.
The Siren is a lightweight next-to-skin layer. It’s crafted from 150gm merino jersey corespun fabric that’s lighter than most other fabrics we use, and is made with a snug, slim fit that works perfectly as a cosy piece beneath your other layers. Our Siren tees fit tighter than other tees in our range, just size up if you like a looser fit.
Standard delivery: free for all order over £ 40. Delivery in 5-7 days, from Monday to Saturday, during working hours.
Please visit our Delivery page and find out more about the ways in which you can receive our products.
You have 30 days from delivery to follow our quick and easy return procedure.
Overall rating: 4.6034756 / 5 from 633 reviews.
The 150 Siren Sweetheart is praised for its lightweight layers, perfect fit, and flattering appearance. Customers appreciate the softness and comfort, though opinions on the fabric vary. The high quality and versatile design make it a great addition to any wardrobe.
Review topics: ["fit","size","weight","price","delivery","quality","feel","problem","material","looks","top","colour","layer","sleeves","fabric","shirt","wear","neck","warmth","base layer","style","comfort","winter","neckline","weather","arms","stretch","icebreaker","medium","shape"].
"Love the neckline and cut of this top but definitely size up! So comfy, slightly stretchy, little more durable than some of the super lightweight fabrics."
— Melissa (5/5)
"Perfect everyday shirt. Could be a little longer."
— Tamara (5/5)
"Perfect breathable layer for my hike"
— Vp (5/5)
"For years I wore uniqlo heat tech shirts, but those would get sweaty and stretch out over time, and I would get too hot in them. This shirt is much nicer on the skin as it never made me sweaty and stays fresh for much longer. I lost my shirt and was devestated—and have since bought a new one. I like that the cut of these shirts are low enough that they’re usually not visible underneath other items, and if I do end up taking a layer off I think the neckline is really beautiful and flattering. I do wish the shirts were a bit longer so they could stay tucked in better. I bought a size small (my usual size, with a chest size of 34b) and it fits well, fitted without being tight."
— Lucia S. (5/5)
"Great base layer in charcoal. Grey is a little sheer but fine if you wear with a bra underneath. Hugs all the right places."
— Mark (5/5)
"Warm stretchy comfortable and moisture wicking. Used 4 days straight on ski adventure and it didn’t stink! Love this thing."
— Anonymous (5/5)
"I live in Icebreaker base layers 9 months a year. I live in a ski town and the warmth breathability and skin feel is the best!!"
— Anonymous (5/5)
"Well made. & super comfy. Staple in our place for everyday wear."
— Anonymous (5/5)
"Exactly what I wanted. I wear this on days that have temps ranging from 40 F to 65 F and I never feel cold or hot. Minimal odor retention great fit. I will be buying more. No complaints. Great price. Great for everyone from beginner to expert. Cold to hot this is the top for you and the whole family. I will be buying other models from Icebreaker! Minimal sweating and stank what else could you ask for?"
— Anonymous (5/5)
"Perfect for base layering under sweaters with low or wide necklines. No visible logo/brand name, which I prefer."
— Alaina 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 | 33-35.5 | 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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