A perfectly tailored suit is appropriate year-round—it’s the fabric that’s seasonal. While heavy wools and tweed jackets look fantastic in the winter, they’re nothing short of suffocating in the warmer months. For spring and summer, opt for lightweight layers that you can wear inside and out, during the day and at night. The key to not sweating is all in the material (and the color; think lighter and brighter). Here’s what to look for.