This top needs to be skin-tight to function correctly. X-Bionic claims thermal properties to heat you up when you are cold, with features that will stop you overheating. I assume this relates to the diff erent fabric panels, which include a fine, almost mesh-like construction at the back and under the bra and arms, and different panels over shoulders and torso. A few brands off er variations on this claim but, in reality, I didn’t notice any heating or cooling eff ect and still felt chilled when wet. The fabric moved sweat effi ciently from my skin, although the high nylon and elastane content made it slower to dry compared with polyester or polypro. Wide cuff s and hem helped resist the automatic roll-up of some tight layers. I found the crew neck, which pressed on my throat, rather high for comfort. The sleeves were too long for the body so, to avoid rucking around my elbows, I had multiple layers around my wrists. A relatively low-pong choice for moderate conditions.