Smartwool Intraknit™ Thermal Merino Base Layer

Review by Erin Trail

Initial Impressions

The Smartwool Intraknit™ Thermal Merino Base Layers are lightweight and super-moveable top, made for all of kinds of extreme cold-weather activities.  The top and the bottom are made from Merino sports yarn and features gender-specific ventilation areas for better thermoregulation and moisture control.

Detailed Review

I’ve been a Smartwool base layer wearer for a long time and was excited to try out the latest and most high-tech base layers for this winter’s ski season.  These are wool base layers, but turned up a notch (or two) to make them appropriate for demanding and high-performance activities.

Features

• Engineered construction uses knit structures to enhance performance with lighter weights and cleaner finish
• Merino Sport yarn combines the power of Merino with the durability and fast dry times of polyester
• 3D mapping results in near custom fit and freedom of movement while ribbed elbows provide added durability
• Mesh ventilation seamlessly knit in gender-specific zones designed to keep the body dry and comfortable

Fit and Function

I wore the Smartwool Intraknit Thermal Merino Base Layers on a winter solstice bikepacking trip in Fort Collins, Colorado and on several ski days where temperatures ranged from 5 to 25 degrees.

I got a size medium (top and bottom) and found the bottoms to run a bit small.  The waistband is a thicker material and is wide, which doesn’t have a lot of give.  Depending on your personal preference and body type, you may want to order up a size to have a bit of room. I found the top to be true to size for a form fitting piece of clothing. If you like a roomier fit, you may want to size up on the top as well.

I found the texture of the Smartwool Intraknit Thermal Merino Base Layers to be very different from other wool base layers that I’ve owned. The ribbing and ventilation makes the fabric feel a bit stiff on the outside, and a bit stiff while wearing it and hanging out.  The inside is soft, but also a bit scratchy.  After a few washes, I did find that the fabric got softer and more flexible.  I would imagine that over time, these layers would continue to get more comfy and “lived-in”.

I wash my base layers in a top loading machine on delicate.  I did notice that I already have a run in the bottoms after around 5 washes.  So if you machine wash these, you should put them in a garment bag, or better yet, hand wash them.

As for function, I really enjoyed wearing them.  The sport yarn and reinforced areas gave my body a bit of extra support while skiing. I found that they breathed very well and maintained my temperature over a variety of mountain conditions. The tight fit didn’t bother me an I appreciated a bit of compression in my legs over long powder days.

Smartwool offers the Intraknit™ Thermal Merino Base Layers in a variety of fun colors and patterns, making these a fun and stylish option for both on and off the slopes. I could easily wear the bottoms as leggings around town or the top as a layering shirt.

Closing Thoughts

The Smartwool Intraknit™ Thermal Merino Base Layers are stylish and technical layer for cold climate activities.  These layers have more structure to them than other base layers, but the structure aids with performance (compression) and moisture management. The fun colors make them appropriate to wear off the slopes.  These do fit tight, so if you want a more generous fit, order up a size.

Erin Trail

Erin Trail’s hobby is collecting hobbies. She’s a 5th Generation Coloradan and grew up exploring the outdoors on family camping trips and hikes.  Her first backpacking trip was at eight years old to Grizzly Reservoir – she proudly carried all of her own gear those 3 miles from the main parking lot to the Reservoir.

Erin is an adult-onset athlete who started as a Masters Swimmer and then developed into a triathlete.  She completed 5 Ironman races and nearly 20 x 70.3 distance Ironman races, including the World Championship in Lahti, Finland, in 2023.  Somewhere along her triathlon journey, she picked up a deep love of cycling.

Cycling encouraged her to see landscapes in a new way, learn new skills and to develop self reliance; now she often goes and does Type 2 rides just to see if she can do it.  She’s got all the bikes: gravel, mountain, fat bike, time trial and road.

She is even known to combine her love of camping and cycling and go off on solo 24 hour overnight bikepacking trips in the mountains of Colorado. In addition to bikes, she teaches yoga, lifts weights, skis, SUPs and has recently purchased a campervan.

Erin is a former Montana park ranger with a degree in environmental engineering.  She loves getting into technical details while putting her gear (and herself) through the paces. She shares her home in Colorado with her husband, Will, and her 3 cats (Zipper, Brewtus, and Simcoe).

2025 brings some exciting things.  Erin has qualified to be on Team USA for USA Triathlon and will be competing in a World Championship off-road triathlon in Pontevedra, Spain in June. To prepare for this event, she’s got several mountain bike races and training weekends planned in the months leading up to the big day.  Additionally, she’s racing Ironman Boise 70.3 in July.  Once her race schedule closes out in July, she’ll be moving to more adventure based activities (bikepacking, vanlife, and mountain bike festivals).

When not adventuring, she can be found on a sunny patio somewhere, drinking beers with her husband.