Thermal long sleeve jersey's offer more use cases than one would expect. While a key component to winter riding, the Specialized Prime-Series Thermal Jersey can easily be a condition dependent 3-season garment. Although it allows air infiltration when exposed, this may be fine on a 60 degree day in light sun, or when combined with a vest for core protection. The same principle applies to a shoulder season ride where a light jacket is carried along. So, it doesn't have to be just a winter option.
The essential element of this thermal jersey is it's 4-way stretch, Polartec® Power Grid™ fabric. It has exceptional thermal capabilities despite it's low bulk and light weight. The Polyester/Spandex Knit blend generates targeted touch points to manage moisture while the grid design and advanced compressibility creates improved breathability and air space for retaining more heat per square centimeter. The inner surface is soft, and eases moisture away from the skin passively and with body movement. Many fabrics employ this concept, but struggle to get one crucial aspect right: the outer layer must allow and encourage the moisture to escape. For the hydrophilic next-to-skin surface to absorb sweat and transfer it to the outside of your garment, as Power Grid™ does, the fabric's outer surface must be properly engineered to disperse moisture for fast evaporation, or the moisture holds closer to the skin and negates the thermal purpose of the garment. If you take it a step further, if you layer over the jersey, especially if close fitting, that layer must also speedily wick and release moisture for the combination to be effective.
The fit is Slim, as the fabric must rest on the body to be optimally effective, but the 4-way stretch afforded by the presence of the Spandex Knit keeps it comfortable and allows movement. The same can be said for raglan sleeve-shoulder design, for greater range of motion without affecting fit. The design team also used anatomically informed panels to achieve a well coordinated piece. The long sleeve thermal jersey also carries a full length zipper for easy on-off, as well as a way to manually regulate core temperature. As a true cycling jersey with the flexibility to be worn without an outer layer or layers, the pro-style rear 3-pocket system is available to carry snacks, tubes, etc. When you take it all into account, especially the use of the truly effective Polartec® Power Grid™ fabric, the Specialized Prime-Series Thermal Jersey should occupy an obvious place in your closet 8-9 months of the year.