Base layers are like underwear – they all seem conceptually the same until you try really nice stuff and really cheap stuff in quick succession. Castelli’s long sleeve Iride Seamless is really nice.
True to its name, the Iride features a seamless torso; a single tube of polypropylene fabric wraps the upper body. The arms have a single seam running underneath. The layer is thin, and certainly tight enough to wear under a snug-fitting jersey.
More remarkable than the construction, however, is the feel. The soft hand is complemented by the snug feel. Off the bike, we ran a half marathon in the Iride and were comfortable the entire time. Read: no friction.
One downside is that the wrist areas are baggy relative to the skintight remainder of the piece. This could be because our test sample didn't have thumb loops to pull the sleeves down, although some models do.
The polypropylene does a good job of moving moisture away from the skin, though, and the garment's antimicrobial properties fight odor well.
The Iride Seamless comes in three sizes (92cm to 110cm chest) and in black/maroon or pink.