Undertop Power Stretch®

Rated 5.00 out of 5 based on 5 customer ratings
(5 customer reviews)


The undertop is the unsung hero of adventure wear: a body-hugging base-layer to keep your core happy during the coldest workouts. It’s ideal for just about everything, including chilling by the campfire when your day is done. You may recognize its super thick, plush material as the same stuff in our performance crops and performance tights. So basically, if you wear them together, you’re not only the warmest person outside, but the coziest.

Made in Massachusetts, USA


Textile:Polartec® Power Stretch® single velour

  • also used in performance crops, undertop, base top, and winter bra lining.
  • content: 49% Poly, 38% Nylon, 13% Spandex
  • strengths: insulation, abrasion resistance, moisture transfer, wind resistance, light weight and water shedding
  • This textile was developed to maximize the garment’s range of motion. The majority of elastic base materials can stretch during movement, but lack the tensile strength to recover their original shape and eventually become permanently damaged. By utilizing elastic fibers with enhanced resilience in our stretch construction we made a performance-fit base fabric that can handle the pressure of demanding physical activities.

Construction techniques:

  • Flatlock
  • Overlock
  • Top Stitch finishing

Additional information

Weight .7 lbs

XXS (0), XS (2-4), S (6-8), M (10-12), L (14-16), XL (18)

Safety Features

Rear reflective bars

Caring for your c2

Although it’s totally fine to wash and dry your c2 with your other active wear, we have found a few care details to be helpful in keeping it looking good for as long as possible:

1. Avoid washing c2 with cotton or other lint shedding materials
2. It’s best to wash synthetics with other synthetics
3. c2 air dries quickly, so save a dime and the environment and let it dry naturally
4. Turn your c2 inside out before washing or drying to protect the outside from zippers and velcro

5 reviews for Undertop Power Stretch®

Jessamyn Anderson
Rated 5 out of 5

I love this top! I have been wearing the Undertop on my early morning rides. It’s very windy where I live near the ocean so it helps keep the cold out. I am so happy with it. Thank you C2!!

Mary Hayes
Rated 5 out of 5

This is my go-to top for early morning rowing. It keeps me comfortably warm, yet I never overheat or get soggy as the sun rises and the day warms up. C2, you are the best!

Rated 5 out of 5

Love, love, love this top! I got it last fall and it remains a steadfast go-to choice on chilly running days. It’s also super cozy next to skin as a sleep top while backpacking – especially when the weather is unseasonably colder and my bag not quite warm enough ;p

Rated 5 out of 5

Not only is this the most comfortable piece of workout apparel I own, but it’s also the most deceiving. I thought because it’s sleeveless that I would have to pack on more layers. Quite the contrary. This tank with the C2 sports bra goes A LONG WAY. Lots of freedom to move the arms and stay warm while outdoors.

Joni Taylor
Rated 5 out of 5

I feel like I opened a pot of gold for my winter wishlist to stay outside no matter how cold it gets. Fitted warmth with no movement restrictions for those days where you see all your pals post that they are on the treadmill or the trainer, and you’re like, “I am outside running in the snow/rain/frozen temps!” I am not a paid athlete. I run and ride because I love to be outside testing my mettle. This base layer is a surprisingly perfect piece to add warmth to your core, but not overheat. No chafing. No soggy skin, and this fabric is such that you don’t feel it. I have been comfortable in 0 degrees and 40 degrees (and this was on one run so starting temps and finishing temps were both comfy. Thanks for such a fabulous product! Love the easy care as well. I am 5’2″ and 107lbs and I have a size XXS if this helps trying to decide on sizes.

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