The Zero RH Thermo Duo skull cap delivers a surprising amount of warmth for its relative lack of bulk, making it ideal for keeping the noggin toasty on cold winter rides.
Constructed from five separate panels, the Thermo Duo manages to successfully tread the fine line between coverage and unnecessary material, at least for my averaged-sized head. The sides dip down slightly and completely cover one's ears, keeping them warm and preventing heat loss. When lining the front hem up with the rim of the helmet, the rear section comes down far enough to provide warmth without causing any bunching when in an aggressive position on the bike. All in all, I couldn't have asked for a better fit.
The material itself is quite stretchy, which enables it to be tugged into the right place, and is lined with a fleece material for warmth. In use, I found that the Thermo Duo was good up to temperatures of double figures, while I never really found its lower temperature limit. Though Zero RH don't make any claims about the material, I found it to be quite windproof and never experienced any issues when descending quickly.
Despite the warmth factor, the material is still quite thin, so it won't cause any issues with helmet compatibility. I sometimes find that I have to adjust my helmet straps to account for the increased helmet height, but this wasn't the case here.
The Thermo Duo is available in white and red as tested, or in three other combinations of white and black. Given that it will be used during winter for the most part, I would've gone for the black option myself, as the state of the local roads means that these things get dirty quickly. That said, I've used the white/red option on a couple of mountain bike rides and it has come out the washing machine looking none the worse for it.
Some reflective details are included on the sides, but these are only really visible if using the skull cap without a helmet.
At £28 full retail price, the Thermo Duo is definitely on the expensive side, even taking into account its fit and function – after all, it's still just a skull cap. However, with a bit of searching, it can be found for closer to the 20 quid mark bringing it more in line with the competition. At this price, I'd highly recommend it.
A well-fitting skull cap which provides enough warmth for all your winter needs, albeit at a cost that puts it above much of its direct competition.
road.cc test report
Make and model: rh+ Thermo Duo Hat
Size tested: L/XL Red White
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 Thermo Duo is a skull cap intended to be used under the helmet in cold weather.
Tell us some more about the technical aspects of the product?
Constructed from five panels with slightly dipped ear sections. The material is fleece lined and provides a degree of windproofing without much added bulk.
Some reflective stripes are included on the sides, but these are only visible without a helmet on.
The flatlock seams aren't the definition of perfect but I've had no issues with them so far in two months.
Fits well and keeps the head warm.
2 months in and it shows no signs of wear. The white colour is still white which is a surprise.
The Thermo Duo is low in bulk for its weight and easily fits underneath the helmet.
Fit and fabric combine to make it warm and comfortable for a wide range of temperatures.
At RRP the product is very expensive, but it can be found cheaper if you look around.
Tell us what you particularly liked about the product
Tell us what you particularly disliked about the product
Did you enjoy using the product? Yes.
Would you consider buying the product? Not at RRP.
Would you recommend the product to a friend? See above.
About the tester
Age: 22 Height: 190cm Weight: 69kg
I usually ride: Canondale EVO Red My best bike is:
I've been riding for: Under 5 years I ride: Every day I would class myself as: Semi pro
I regularly do the following types of riding: road racing, time trialling, cyclo cross, commuting, mtb,
For 5 years, racing was my life and I went all the way from a newbie bonking after 40 miles, to a full-timer plying my trade on the Belgian kermesse scene. Unfortunately, the pro dream wasn't meant to be and these days, you're more likely to find me bimbling about country lanes and sleeping in a bush on the side of the road.