The TrailTech Shell Jacket solves the emergency-shell dilemma for trail runners: pack a rain layer or run light, never both. A 5-micron PU membrane sits inside a 3-layer Japanese fabric and holds a 20,000mm waterproof rating at just 45 grams per square meter, so the shell weighs 4. 5 ounces in a men's medium. The seams are fully welded rather than stitched, so the waterproofing holds at every panel line instead of just across the face fabric. That construction is what lets a shell this light double as real storm protection instead of a backup layer. What Our Gearhead(R) Experts Are Saying:"I got caught in a ridge-line downpour four hours into a long run with nothing but this jacket clipped to my belt, and I stayed dry through the whole descent. That's the only test that matters for a shell this light."