Assos Thermobooster P1 base layer review: The base layer that doubles as a jersey

I got very excited when I pulled the Assos Thermobooster base layer on at the start of the winter. It's a brand-new addition to the Assos line for this winter and despite looking like a long-sleeved, full-zip jersey, this piece sits in the Swiss brand's base layer range. 

It’s very sleek and stylish, close fitting and light. The single, simple white Assos roundel on the shoulder stood out, and I thought ‘I can’t wait to get out in this’. 

The Thermobooster is designed to be worn as a lightweight, fast layer over a summer base layer or jersey for intense riding, or as an additional base layer as part of your winter layering system, going under a heavier jacket or jersey to add warmth. It comes in one colour, black, and has a RRP of £175 / $225 / €200.

As I mentioned in my recent Assos LS Winter Skin Layer review, Assos is about high-quality, technical kit that’s often quite specific, it’s on the expensive side, but it’s usually easy enough to see or work out where that extra spend goes. 

Head to my best cycling base layers guide to see a best of the best roundup of winter and summer base layers all in one place.

Design and Aesthetics 

The Thermobooster comes in one colour; black. Whilst Assos is updating and diversifying its product ranges with brighter designs, this is classic Assos for me. 

There are minimal logos or wordmarks just the single white rubber Assos roundel that I mentioned on the left shoulder and a small Thermobsooter badge at the neck, the round metal zipper is also in the shape of the Assos 'A'. 

The base layer is constructed from a Polyester / Elastane mix and is thin and light. I wear a small in pretty much everything, but am wearing a medium in the pictures. Check your sizing, but if you wear a small you will probably want to size up here. 

The body of the piece uses what Assos has named 'Skuba', which the brand says is a ultra stretchable textile that is soft and aerodynamic whilst maintaining breathability. There are often some unfamiliar technical words around Assos kit, but it's easy enough to get your head around it all. The inside of the piece is indeed really soft and comfortable, it's very nice to wear indeed. 

Next up are the 'Sonic-SN' arms, another breathable aero textile. In plain speak the arms have a similar finish and feel to some aero cycling gloves or even aero socks. They are a couple of millimetres thick and are both soft and comfortable. The wrists and hem of the Thermobooster have a raw cut finish, which helps them look extra clean and slick.

The last bit of Assos tech to go over is the 'StruzzoKragen' collar textile. You will see in the pictures the extended neck section - it's similar to the material on the arms, again soft and plush, but Assos claims it will help regulate your temperature without the need to unzip. This mirrors my colleague's experience with the Assos Equipe R Habu winter jacket. 

Finally, there are two good-sized mesh rear pockets for when you are wearing this base layer as an outer layer. I've carried a down gilet comfortably on one side for example, but you may find yourself wanting more space if you really load up with supplies and spares, but this isn't really what the Thermoboster has been designed for.

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Performance 

Assos cites two uses for the Thermobooster; as a lightweight outer layer for intense riding, and as an additional base layer to boost warmth on cold days. I have used it for both applications and it has performed very nicely. 

I can hear some of you at the back saying 'It's a thin long-sleeved jersey, Tom, they have been around for a while'. I agree, you could call it that, and wear it as such. Assos however really examines the details, and in use, it's obvious what it is trying to achieve here with the Thermobooster's dual purpose USP. 

In the autumn I wore it for several weeks straight on my Saturday morning chaingang over a range of short and long sleeve base layers. The ride has an early cool start, but I work really hard on it and need to be light and aero on the bike. The Thermobooster was perfect for this, I could carry my phone, pump, gel and keys in the pockets and felt fast (and stylish) on the bike, it also breathes well and was the perfect tool for the job. Big tick from me there, if you're going hard, doing efforts, etc in it, you will be very happy.

I've also used it under a Castelli Perfetto jacket and over a long winter sleeve base layer for three hours steady at just above freezing. It's thin and stretchy meaning it layers well without causing restriction and acts as an effective mid-layer.

There's a third use for me, which is just as a thin, lightweight and stylish long-sleeve jersey for whatever you want to use it for, there are no hard rules here. Carry it just in case in a pocket, it folds down well, or wear it on a spring or summer morning because you want to. It would do very well under a gilet on cooler days too. 

I've had no quality issues, and the Thermobooster has washed well at 30 degrees for me, it hasn't put a foot wrong. 

Value 

This is an expensive piece of kit, but I'd imagine most people browsing for Assos kit are aware of the generally high prices and know what they want. 

As I often find with Assos, depending on the piece, the design choices, materials and fit add up and result in an elevated level of comfort, fit and performance. They may not smack you in the face straight out of the gate, but it doesn't take too long to work it out. 

If you do invest in the Thermobooster I don't think you will regret the outlay. It's a lovely thing to wear and ride in and hasn't put a foot wrong for me so far. 

Verdict 

I love wearing the Thermobooster, for me, it really shines on those high-intensity rides when I want to be light and aero on the bike. Aesthetics and style are a major concern for cyclists who don't get given team kit to wear, and I love the sleek, subtle styling as much as the fit and performance.