The Gore Windstopper Helium fabric used in Castelli's Fusione jacket does an excellent job of doing just that: even the iciest of breezes are stopped dead in their tracks, providing just that extra measure of warmth right when you need it. A DWR coating helps shed rainwater and road spray too, though since the seams aren't taped we wouldn’t consider the Fusione to offer proper protection when storm clouds roll in.
The cut is very good, with just enough room in the body and sleeves for a couple of layers plus an elasticized hem, Velcro cuffs, and a clever, fuzzy flip-up collar to protect the back of your neck if needed. Though the fit isn't particularly snug, the slightly stiff material doesn't flutter in the wind at high speeds like with some wispy, ultralight shells we've used in the past.
Breathability is only so-so, however, and it doesn't take long before things get clammy if you're putting in a good effort, especially around the forearms. Thankfully, two pairs of well-placed, mesh-backed vents – one set at the middle of your chest and the other down the length of your back on either side – are on hand to help clear out the excess humidity.
When everything's opened up you can feel a breeze passing through and it's quite effective at keeping your torso dry. Even so, we still wished for another set of vents or even some permanent mesh in the forearms to further expand the comfort range, though one could loosen up the cuffs to help bring in some air.
Those back vents are exceptionally easy to open thanks to a clever lanyard system that provides a massive target when you reach back with your hands. But they're easier to open than close fully. In case things really warm up, the Fusione is compact enough to fit in a jersey pocket but only just so – you'll need to roll it up tightly so don't count on just hastily stuffing it in while rolling along in a group.
Castelli have decided that the Fusione can go without pockets – something we were willing to live with since this jacket is meant to be worn over a jersey and not by itself, but something to keep in mind nonetheless. What Castelli haven't skimped on, however, is nighttime visibility as there's lots of reflective piping stitched in throughout to help drivers see you come sundown.