Icebreaker  Siren Sweetheart Long Underwear Top - Women's

$90.00
Members get an est. $9.00 in rewards

Ideal for year-round use in traveling, hiking or relaxing after a big day outside, the Icebreaker Siren Sweetheart top is soft and stretchy with an updated fit and fabric that make it even more comfy.

Color: Midnight Navy
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Members get an estimated $9.00 (10%) back on this item as a part of your annual .

Members get an estimated $9.00 (10%) back on this item as a part of your annual .
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Features

  • Corespun fabric: soft merino wool fibers are wrapped around a nylon core for strength and durability, while retaining next-to-skin softness; Lycra® spandex adds stretch
  • Updated with an improved fit over last season
  • Sleek design and a flattering neckline for everyday comfort and layering
  • Icebreaker will replace your garment within 1 year of purchase if it has been damaged by faulty fabric, stitching or manufacturing; see Icebreaker website for details

Imported.

View all Icebreaker Women's Base Layer Tops

Technical Specs

Best Use

Casual

Shirt Type

T-shirt

Fabric

83% merino wool/12% nylon/5% Lycra spandex

Moisture Wicking

Yes

Underwear Weight

Lightweight

Sleeve Length

Long Sleeve

Gender

Women's

Reviews

9 reviews with an average rating of 4.4 out of 5 stars

71% 5 of 7 reviewers recommended

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Customer Images

Triana
Location:Cayucos, CA, United States
Rated 5.0 out of 5 stars
8 years ago

Can't take it off

I love this shirt!! I honestly have been wearing it almost every day this winter. Perfect for hiking or just an everyday shirt to keep you warmer. Stylish and comfortable! I ordered XS I'm about 5'4' 115 pounds

Lucia S.
Rated 5.0 out of 5 stars
1 month ago

Perfect base layer

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.

Vp
Rated 5.0 out of 5 stars
3 days ago

[This review was collected as part of a promotion.]

Philippa
Location:Somerset
Rated 5.0 out of 5 stars
1 year ago

I would buy more if there were more colours that suited me.

[This review was collected as part of a promotion.] I really love the weight and warmth of this top and have two others in different colours. Would buy more of them if there were more colours. Perfect to put in a bag as it folds very small so handy extra layer even in a small handbag or on a flight.

Mkatt
Location:Albany, NY
Age:55–64
Weight:125–150 lbs.
Height:5'4"
Rated 4.0 out of 5 stars
8 months ago

Wide open neckline.

The neckline is pretty wide open and the body fits close. I got my usual size medium, and it's very close-fitting though not tight. It feels a bit itchier than the Icebreaker merino 200 oasis crewneck.

Age:55–64
Weight:125–150 lbs.
Height:5'4"

Overall Fit Rating

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H
Location:London
Rated 4.0 out of 5 stars
1 year ago

Useful under layer

[This review was collected as part of a promotion.] A lovely top -with a good boat neck so yu can wear it under tops without it showing. Only downside is horrid scratchy label sewn in to side. Had to undo seam to remove it and then sew it up again.

Furryjen
Location:Devon
Rated 2.0 out of 5 stars
1 year ago

See through!

This came in a box labeled "underwear". As such, it would be fine but NOT as a long sleeved t-shirt as it is way too see through. Such a shame as it is a lovely colour and fit.

wolf
Location:London
Rated 5.0 out of 5 stars
1 year ago

another great Icebreaker garment

[This review was collected as part of a promotion.] A gift for my partner. We have been wearing Icebreaker for years. This is a great looking top with a feminine cut.

Me
Location:Derbyshire
Rated 5.0 out of 5 stars
1 year ago

Just what I was hoping for

[This review was collected as part of a promotion.] The top is neat, comfortable and keeps me warm. I use it under normal clothes on very cold days.

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