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The DeFeet UnDWool is a really warm base layer yet is thin enough to comfortably sit beneath several layers without adding much bulk. The price does place it at the upper end of what we'd expect to pay for a base layer though.
The base layer is made from Merino wool which is my personal favourite base layer material when it comes to keeping warm in the winter. This is quite a thin base layer so it will serve you well in warmer temperatures, but the insulation provided is decent consider how thin it is. It's a very fine wool, and is exceptionally soft next to the skin.
Incidentally, DeFeet gets its Merino from sources that don't practice mulesing of the sheep, a controversial technique of preventing fly larva infection that some campaigners say is cruel.
Despite its lack of bulk, DeFeet pitch this as their warmest base layer in its UnDSystem range, and my testing certainly backed this up. On a recent ride with a temperature hovering between 5°C and 7°C, and just a lightweight softshell over the top, I was adequately warm.
Fit is important in a base layer and in this respect the DeFeet does well. I'd describe it as a slim fit. The size medium tested isn't skin tight, instead there is a bit of bagginess which increases the comfort. And also means you can wear it off the bike as a t-shirt quite happily. The length is generous so that you get a nice underlap with your shorts or tights.
I tested the short sleeve version, which is a more versatile option than the long sleeve version that is also available, though for the coldest winter days the longer sleeves would be an obvious bonus. The construction uses raglan sleeves designed to eliminate uncomfortable shoulder seams. Certainly none of the seams are noticeable when you're wearing it.
There's very little branding, just the small DeFeet logo on front of the collar.
Soft, comfortable and warm merino wool base layer.
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Make and model: DeFeet UnDWool Base Layer
Size tested: Medium, Black
Tell us what the product is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?
The warmest base layer in the UnD line of cycling specific base layers. UnD Wool is available in both short or long sleeves. Made with the absolute finest Merino Wool available. When it's cooler out, there is significant elevation change, or there is moisture in the forecast, you'll be glad you packed the UnD Wool™. When the ride is over, throw it in the dryer and wear it with jeans out on the town.
Tell us some more about the technical aspects of the product?
UnDWool™ is simply the finest wool base layer ever crafted for cycling. Made from non-mulesing merino wool that is soft against the skin and doesn't itch. UnDWool™ is the go-to base layer any time there could be moisture on the ride or the temperature is south of 60 degrees. In the case of both of those happening, don't leave home without it! As a bonus, looks great with a pair of jeans. Certified Woolie™.
The UnDWool is the warmest base layer in the UnDSystem. DeFeet knits the highest grade wools on the planet into a special fabric that is thin, elastic, soft yet durable. Adorning the front of the collar is a small, woven "D" logo label. We were so thrilled with the UnD Wool we couldn't resist adding this signature of class, like the bolting on of a head tube badge to finish a fine custom frame.
Tell us what you particularly liked about the product
Really soft merino wool, thin yet warm.
Did you enjoy using the product? Yes.
Would you consider buying the product? Maybe.
Would you recommend the product to a friend? Maybe.
Anything further to say about the product in conclusion?
It's a very nice base layer but there are cheaper merino wool base layers availablen — even Rapha's costs less. If you're not worried about the price it's a high quality base layer that works well.
Age: 31 Height: 180 Weight: 67
I usually ride: My best bike is:
I've been riding for: 10-20 years I ride: Every day I would class myself as: Expert
I regularly do the following types of riding: road racing, time trialling, cyclo cross, commuting, touring, mtb,
David worked on the road.cc tech team from 2012-2020. Previously he was editor of Bikemagic.com and before that staff writer at RCUK. He's a seasoned cyclist of all disciplines, from road to mountain biking, touring to cyclo-cross, he only wishes he had time to ride them all. He's mildly competitive, though he'll never admit it, and is a frequent road racer but is too lazy to do really well. He currently resides in the Cotswolds, and you can now find him over on his own YouTube channel David Arthur - Just Ride Bikes.