Castelli Flanders 2 Warm LS Base Layer Review: a cosy layer perfectly suited to wintry days in the saddle.

The latest version of the Flanders Warm base layer, named after the home of Belgium’s infamous Spring Classic, doesn’t disappoint. It’s exceptionally comfortable and performs on par with merino during rides. However, it doesn’t manage odours as well as merino, meaning it’ll likely head straight to the laundry basket after most outings.

Construction

The Flanders 2 W Warm Baselayer is made with a multi-denier, 100% polyester fabric, which the brand calls SottoZero Fleece - translating to “sub-zero fleece”. This technical fabric has a soft, brushed interior, intended to trap warm air and manage moisture effectively.

Flatlock seams have been used throughout. The layer also incorporates mesh inserts under the arms, designed to boost airflow and prevent overheating. The medium-height collar adds extra coverage.

In terms of fit, I typically wear a size medium across most cycling brands, very occasionally opting for a large. However, I was surprised to find I needed to exchange the medium I was sent for a small. With sizes ranging from XS to XL, my advice is to select with caution.

The ride

The first thing you notice about the Flanders 2 Warm is the cosy, brushed interior - it’s exceptionally soft against the skin. The fabric has substance but doesn’t go so far as to be weighty - the substance comes from the fleecy inner. Combining these properties with the flatlock seams creates a base layer that feels incredibly comfortable, giving a reassuring sense that you’re properly dressed for a cold winter training ride; Flanders, here we come... In reality, the UK shares the same winter conditions as the Flemish-speaking part of Belgium, so the base layer is perfectly suited to training in any part of the UK.

Despite having exchanged the size medium for a small, I still found the layer relatively loose around the torso - the photos show this well. The sleeve and body length are both generous - something I personally appreciate, though this may not suit every female rider. The fabric is in no way restrictive, so if you prefer something that hugs the body, you should be safe sizing down.

The layer performs exactly as Castelli claims; it provides excellent insulation. I wore it in temperatures down to 2°C/36°F and felt more than warm enough. The raised collar is really well judged for chilly days. In those low temperatures, there was no major moisture build-up, undoubtedly helped by the underarm mesh panels. Yes, if I rode tempo for a prolonged period of time, I would sense sweat, but the layer never got uncomfortably damp.

Castelli suggest a performance window of -2°C/ 28°F to 10°C /50°F. In my experience, the upper limit is not realistic. Unless I was putting in zero effort and teaming it with a very lightweight long-sleeve jersey, it was overbearing in anything above about 7°C/ 45°F. The raised collar exacerbates heat build-up in these temperatures too. I tried it in temperatures nearing double figures and with a moderate effort found the moisture build-up unpleasant, with the top becoming rather damp and clingy. For me, the window of performance would be a more conservative -2°C/ 28°F to 7°C /45°F.

While the warmth it provides is comparable to wool, the fabric’s ability to handle odours is certainly not on par with wool’s. I found it needs to be washed after every ride; body odours love it.

Value and conclusion

The £90/$130 RRP is premium and considering that it needs very frequent washing, the cost per wear is high. Investing in merino might be a better choice in the long term. I recently reviewed an option from Sportful, while I don’t think it is as warm as Castelli’s, with less laundering it would provide better value in the long run. However, if you don’t tolerate wool, the Flanders 2 Warm is probably the best alternative you’re likely to find.

I’ve loved testing the layer and will continue to pull it out for training rides on very cold days. For anything milder, I’ll be opting for a layer that doesn’t cling to odours quite as readily.