There are countless weather problems that every cyclist has to prepare for during the fall, winter, and spring. For rain, you'll want a rain jacket that doesn't make you overheat. For chilling wind, you'll need a wind blocking jersey, instead. If choosing the appropriate outerwear is among the most important decisions a cyclist can make in the colder months, then choosing the right base layer isn't far behind. Happily for us, when the temperature drops to 10 degrees Fahrenheit either side of freezing, then this second choice is easy: Castelli's Flandria Warm Base Layer with Long Sleeves. The Flandria is made with a durable SottoZero Fleece that insulates and wicks. Dryer, after all, is warmer. Mesh inserts provide ventilation in the underarms, just in case you overheat, and the flatlock stitching and flat hems mean the Flandria will fit comfortably as a piece of layering gear. Castelli recommends it for use in 23 to 46 degrees, and, while this range may seem excessively broad, we find that the Flandria gets the job done in all conditions when layered with the right outer layer. 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. The Flandria Warm's branding is less ostentatious than the basic Flandria jersey, comprising only a simple, non-stylized Castelli with no red scorpion logo. Chances are good that, if conditions call for the Flandria Warm, you'll likely keep your jacket or outer jersey zipped up the entire ride. The Flandria Warm isn't for showing off, it's purely for keeping you warm; however, it will let you accumulate base miles through the coldest months so that, come spring, your legs will be doing all the talking.