The TRAIL Merino Long-Sleeve Jersey runs a body-mapped heavyweight fabric across the front and a merino mesh panel across the back, venting excess heat exactly where a hard trail effort generates it. That zoning holds up through three seasons of riding, whether worn solo or stacked under a shell. What Our Gearhead(R) Experts Are Saying:"I ground up a rocky climb that had me sweating through my base layer in minutes, and my back never felt like it was cooking. Every other long sleeve I own traps that heat right against my spine."