With fall upon us, it's time to turn our attention to preparing for unpredictable and inclement weather. There isn't one jacket or insulated jersey that provides enough flexibility to cover all conditions between September and March, so we typically keep a few options on hand for strategic layering. We find that few pieces of kit offer women more flexibility in this regard than the Castelli Flandria Base Layer. Considering that its namesake is one of the most successful classics cycling teams of all time, this should come as no surprise. The Flandria's torso consists of rib-knitted, multidenier polyester to provide warmth, flex, and durability in the area where you need it most. The sleeves are a more flexible iteration of the torso's durable material, and the underarms feature yet another iteration, this time ventilated to regulate body heat. All three types of polyester used in the Flandria's construction excel at moisture management, so you'll stay dry while grinding intervals or mashing up the occasional hill. The fit is snug and long, with an exaggerated hem and sleeves to ensure no gap in coverage between top and bottom, gloves and cuffs. It's snug enough that you can wear it however you need it: under a jersey in the low 40s, under a jacket in the low 30s, under rainwear -- whatever the situation calls for. Flatlock stitching eliminates any discomfort at the seams and makes this an ideal choice for layering under roughly textured wind and cold-resistant materials. Castelli combines the white and grey fabric with a tasteful logo placement for a look you'll want to show off by dropping your outer layer's zipper a bit when you stop for a mid-ride coffee. The Castelli Flandria Base Layer is available in five sizes from X-Small to X-Large.