Pactimo has a relatively simple plan to handle temperatures between zero and 45 degrees Fahrenheit, and it actually involves very little layering. Up top, Pactimo recommends a very warm base layer—like their High Grade Wool or Thermoregulator—matched to a really warm jacket with zippered vents, like the Vertex WX-D. And that's it. No jersey. If this feels a bit warm, go with a lighter base layer. As you warm up while riding, open your jackets zippers to drop heat and you won't need to worry about shedding layers."