Castelli Insider Bib Shorts Review

Indoor cycling is a big part of the fabric that weaves together the modern cycling landscape. Just as you wouldn’t expect road cycling and gravel cycling to use the same gear, it’s unreasonable to expect indoor and outdoor cycling to use the same gear. Indoor cycling is a unique challenge with unique needs and some of the best companies have risen to that challenge.

If you’re looking for clothing specifically designed to meet the challenges of indoor cycling, then Castelli should be on your radar. We have included several Castelli pieces in our guide to best indoor cycling clothes because it is one of the rare brands to have developed specific equipment. The Castelli Insider Bib Shorts are not a recycled design with a new branding. This is a unique collection of Castelli technologies targeting the needs of indoor riding and we put them to the test. After many hours of sweating through virtual landscapes to see what they look like, we’re ready to talk about it. If you feel ready to stop recycling old bibs or use your best cycling shorts for your sweaty indoor rides, and instead switch to purpose-built gear, keep reading to see what we think of the bike. Castelli effort.

Castelli Insider bib shorts rear view

These blue looking panels are officially black, but the sublimation process means they look more blue when worn. (Image credit: Josh Ross)

Design and aesthetics

The design of the Castelli Insider bib shorts is not entirely unique. It’s unusual for a company like Castelli to completely redesign a model so that this isn’t a problem, or even unexpected. In this case, the design comes from the Inferno bib shorts. Inferno bibs exist for riding in the hottest weather, so it makes sense to start there for a specific indoor bib. The two aren’t exactly the same though.

The most noticeable similarity is the unique Giro Air mesh leg ends. Castelli calls them leg ends, but that’s the only grip material there is on the Insider bibs. They don’t have an additional silicone grip but the inner surface has some grip even without the need for additional material. Castelli manages this by using the higher friction threads in the fabric and placing them on the surface in a specific pattern that allows them to come into contact with the skin. In combination with the reduced side stretch and the tight fit, there is nothing more needed. The band is also wide enough to prevent the thigh from feeling compressed.

Castelli Insider bib shorts mesh leg openings

The mesh leg openings are one of the best parts of the design. They are cool, comfortable and look great. (Image credit: Josh Ross)

Above the mesh band, the front and outer thigh are two panels, both using the same fabric. Although the official color is black, it bears a striking resemblance to the Saville Blue available on the matching Insider jersey. Part of this color discrepancy comes from how Castelli applies color. While some Castelli pieces use a traditional dye, the Insider bib shorts undergo a dye-sublimation printing process. Instead of changing the color of the fibers, the color is printed on the face of the white fabric. Flip the bibs inside out and you can see that these panels are white. When squeezed, this white bleeds through the color and changes what should be a black to a grey/blue color. The advantage of this process is that the logo is printed at once and will never crack or peel – a common complaint on some of Castelli’s other gear.

On the inner thigh and under the chamois you will find a different fabric. It’s a higher nylon content to help it resist wear and tear from saddle contact. It’s also really black, like the mesh grip area, and you can see the color differences in all the different panels.

For the chamois, Castelli opted for the Kiss Air 2 chamois in the Insider bib shorts. You might think that the Kiss Air 2 pad is inferior compared to the Progetto X2 Air, but that’s not really the case. It’s different and while the Progetto X2 Air is better in some situations, the Kiss Air 2 is still one of the best chamois options on the market. It just lacks the Progetto’s freezing pressure point protection. It’s also a bit thinner and doesn’t float freely the way the other cushion does. For shorter rides and higher intensities, like typical workout rides, the Kiss Air 2 makes a lot of sense and might even be the better option.

Castelli Insider Chamois Detail Bib Shorts

The Kiss Air 2 chamois pairs well with the needs of indoor cycling. (Image credit: Josh Ross)


I wear a lot of shorts. I constantly talk about the small performance advantages of one design over another and how brands tell a unique story for one product over another. Like everyone else, when I put on shorts and look great, I’m a fan. This is even true for a specific short inside that no one will see.

In this case though, my perspective of looking good comes from the same design decisions that drive performance. In an effort to make the best bibs for hot weather performance, the legs of the Castelli Insider bibs are short. This means they fall straight into your thigh meat. I’m not a track sprinter, but I like the look of my thigh under the leg end mesh. It’s silly, but I’ll take what I can.

There are other details, actual performance details, which also contribute to my appreciation. I often rave about the decisions of the Castelli chamois and I can do it again when it comes to the Insider bib shorts. I think I would have been just as happy with the Progetto X2 air but in all my time in these I have never felt let down by the Kiss Air2. Spending an hour running, often out of the saddle, isn’t a torture test for a buff, but the Kiss Air2 does a good job of staying out of my consciousness, which is about as good a compliment as there’s enough for a chamois.

Castelli Insider bib shorts mesh upper back

The straps and the back use a mesh that breathes well but does not roll up. (Image credit: Josh Ross)

On the other side of the chamois is another detail that I appreciate. There are no bibs that take more beatings than the ones I wear inside. Despite significant kilometers covered, I very rarely feel the need to retire outside the shorts. Interior equipment, on the other hand, often needs to be replaced and when it comes to bibs, the saddle area is sometimes the culprit. Using a higher wear fabric in the saddle contact area is a choice that makes a lot of sense.

As you move up from the bibs to the suspenders, there is another choice that I appreciate. The radio pocket might not make much sense, but the particular type of mesh Castelli uses for Insider bibs is a good choice. Like the extremities of the legs, this is another area where heat can sometimes build up. Castelli uses different fabrics in different bib shorts to achieve the same ventilation, but for the Insider it’s another good balance of light without constantly rolling up.

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Castelli Insider front and back bib shorts in dyed underfabric

The back of the main fabric on the thighs is white while the front is black. (Image credit: Josh Ross)
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Castelli Insider bib shorts showing different black colors

There are different colors of black in different areas due to construction differences. (Image credit: Josh Ross)


The Castelli Insider Bib Shorts may not be the best indoor cycling option for everyone. Although the design comes from the Inferno warm weather bib shorts, the fabric used is a bit thicker than these bib shorts. Leg ends and suspenders use a lightweight mesh that breathes well but the main fabrics are a bit heavier.

This works well for me because my “pain cave” is cold in the winter. Something like the Assos Equipe RSR Superlight S9 Bib Shorts it’s great when it’s hot but in december and january I need something more substantial. If that’s what you need, the Castelli Insider handles a cold start better while still running when the race gets hot. If you ride indoors in a climate-controlled room, you may want a lighter option. As long as your temperature preferences match, the Castelli Insider Bib Shorts are a great indoor riding option at a great price.

Technical specifications: Castelli Insider bib shorts

  • Price: £130.00 / $139.99 / €119.95 / AU$199
  • Weight: 150 grams in small size
  • Size availability: XS-3XL
  • Color options: Black

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