In working directly with Team Ineos, the Castelli designers sought to build a more comfortable, more variable, more effective arm warmer. The result was the Pro Seamless Arm Warmer, with a wide temperature range, combined with high stretch and seamless comfort to create their most versatile warmer. Ultimately the code was cracked with a combination of a new fabric blend and construction process that allows for the seamless circular knit. The design also had to incorporate zones for greater flex, and relief from bunching, in this case in the elbow zone. When you look closely you can see the fabric knit following the normal arm articulation. The stretch is so effective it relaxes and extends with ease, always returning to form. The upper and lower cuffs ably hold the warmer in place.

Many other warmers on the market are made with a nylon/Lycra® blend that tends to hold too much moisture, but the Castelli designers knew they could get better moisture management with a polyester yarn base. Working with polyester has it's drawbacks, as it makes it more difficult to get the right stretch, return and manufacturing consistency. It took a year longer than the team planned for, the fabric blend and construction came through in the end. These warmers are a favorite of pro riders because they're crazy light and they're extremely warm for their weight, yet even in milder conditions you don't overheat. The Pro Seamless Arm Warmers are so stretchy you hardly feel them on, yet when you take them off they occupy a fraction of the space that normal warmers would take in your pocket.