THIS JACKET FEATURES internally taped seams to keep out the weather, a three-layer construction, and a storm flap covering the main front zipper, again to keep out the rain. Quite simply, it’s one of the most weatherproof training jackets we’ve ever worn. It’s also very lightweight, its thin construction making it possible to roll up and stow in a rear jersey pocket, and it provides an impermeable skin over whatever you happen to be wearing beneath. Although there are only two pockets, the zipped right-hand-side compartment runs the entire width of the jacket’s rear, and there’s an extra pouch on the left, complete with drain holes. The Pro SL’s breathability is unsurpassed in this test, and overall protection is improved further by a very high collar and anatomically-designed stretch cuff. The best outer layer we’ve tested in a very long time.