Base layers are thought to be for keeping warm. When you’re heading out on a ride and a single layer isn’t enough, whether it be a jacket or jersey, you put on a base layer for a little extra warmth. So then why do you see pros wearing a base layer under their short sleeve jerseys during the hot summer months? It turns out base layers do more than keep you warm. A short sleeve or sleeveless base layer underneath your jersey does two major things: 1)keeps your bib straps or jersey from rubbing you raw and 2)keeps your jersey away from your skin. The first reason is an obvious one why it’s a good thing; nobody wants to be on a long ride and have to deal with the discomfort of being rubbed raw. The second isn’t quite as clear-cut. Keeping the jersey off your skin doesn’t allow it to become drenched with sweat and stick tightly to your upper body. Everyone knows how uncomfortable it is to wear a sweat-soaked t-shirt, and having a jersey stuck to you in this same fashion doesn’t exactly allow for peak performance. The base layer creates a pocket of air between your skin and the jersey, which is exactly what’s needed to keep the dreaded jersey-stick from getting you down.
There is obviously an argument that a base layer will only make you hotter on a hot day. I don’t have a scientific answer to say it doesn’t, but what I do know is that if the Cervelo Test Team is wearing them on hot days, they’re not hindering performance. The Cervelo Test Team is arguably the most technologically advanced team on the Pro Tour. They have looked at all facets of the bike and human body, tweaking ever-so-slightly, anything and everything that could created an advantage over other teams. If a summer-weight base layer slowed down the Test Team, they wouldn’t be wearing them.
Every brand has their own take on a summer base layer. To stay with the Cervelo Test Team example, their clothing sponsor, Castelli, makes a sleeveless base layer called the Castelli Core Mesh Sleeveless (pictured). If you’ve ever seen the Castelli scorpion logo peaking out the top of an unzipped Test Team jersey, you’ve seen the Core Mesh Base Layer. The Core Mesh is made with a lightweight mesh-like fabric that allows air through while still providing the layer you need between you and the jersey. There isn’t anything too special about the Core Mesh compared to other summer-weight base layers, but it does everything you need it to and it does it well.