I wanted to get my hands on this ‘onesie’ as soon as Castelli released it.

Their Sanremo Thermosuit is a revolutionary piece of kit based on an obvious idea: to produce an all-in-one, a full-body skin suit for winter weather.

Peeling on the suit in winter is an unusual experience. One of its main selling points is that you only have the one item of clothing plus base layer to put on, and this in itself saves you a good 15 minutes of deliberation before getting on with the business of riding.

Castelli Sanremo Thermosuit - full-length

Castelli Sanremo Thermosuit - full-length

The lightweight feel of the garment is due both to its literal weight and to the lack of under-layering, which leaves you feeling more flexible and comfortable with a sense of freedom of movement not normally associated with going out in the cold.

The fleecy lining and hugging contours make you feel quite at home inside, and genuinely make it easier to get out on the bike, giving cold weather riding a snug and cosy feel. The first few minutes out on the road feel a little unnerving so seemingly underdressed, but as your body begins to generate some heat, the suits gently warms your bones and the temperature inside seems to manage itself remarkably well.

The promotional blurb on this piece of kit talks a lot about ‘moisture management’, and I was dryer in the Sanremo Thermosuit than more conventional winter clothing, avoiding the sweat-chill cycle often associated with trying to get the layers just right.

The bottom half of the suit is based on Castelli’s Sorpasso bib tight and the hollow fibre technology it uses is effective in keeping you warm and dry, although I got the sense that this was enhanced further in the one-piece suit as any ‘hot spots’ from sweaty layers overlapping were avoided.

Castelli have utilised wind stopper technology with a Gore X-lite stretch fabric panel across the front, giving you extra protection where you need it without compromising the fit or weight.

Three pockets at the back provide plenty of room for all winter bits and bobs, and provide a helpful store for spare tubes, snacks and the like close to your body where they are unlikely to jump out if you go over a pot hole.

Castelli Sanremo Thermosuit - pocket

Castelli Sanremo Thermosuit - pocket

There are also a couple of nice details that finish off the fit, like the high neck that is not too tight but gives a bit of extra protection, and the smooth zip “Giro3" ankle grippers, which make it very “fitted", without cutting off your circulation.

The suit is recommended for temperatures ranging from three to 15 degrees and I found this a perfectly reasonable guide. On one occasion, I tested the suit in sub-zero temperatures with ice on the ground and found that with my warmest base layer, I maintained a reasonable body temperature, so long as I was moving along at a decent pace: proof that though it was a little too light for the day’s temperature, it is certainly not a winter lightweight.

In this regard, I think the Sanremo Thermosuit is well suited to the British seasons, and is a really useful item to have in your cycling wardrobe, especially during the transitions from autumn to winter and from winter to spring. I’d pair it with an outer layer only on the coldest days.

At a first glance, the Sanremo Thermosuit's £250 price tag can look like a significant investment, but compared with the combined price of quality tights and jacket, and the potential for additional use over this more conventional combination, I think it’s pretty good value. The Sorpasso bib-tights alone sell for £150, so all together I think the suit comes in at a good price.

Castelli Sanremo Thermosuit - lining

Castelli Sanremo Thermosuit - lining

Because the design leaves no room for adjustment it is especially important to get the right size and it would be well worth trying one on before committing and taking it out on the road. I tested the small and found the fit snug and comfortable.

The “one-sie" may be trendy at the moment, but I don’t believe the Sanremo Thermosuit is merely a fashion item: its performance on the road confirms the mix of technology and craftsmanship that underpins the design.

I would definitely spend my own money on this suit and am completely sold on the winter all-in-one concept, and hope that it attracts enough interest in the general public to stay in the market place for winters to come.

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