RaceTech Tank Top runs on a 63-gram micro dot air fabric that carries UPF 50 sun protection without adding the weight or heat most sun shirts do. Merrow stitch seams and a bonded hem keep the construction low profile, so it sits clean under a running belt or vest instead of creating chafe points. At 63 grams, it disappears on the body the same way a bare torso would on a hot effort. What Our Gearhead(R) Experts Are Saying:"I roll this into my vest for the descent and pull it back on the second I hit an exposed ridge. It packs small enough that I stop noticing it's even in there until the sun comes back."