The Xcelerator is a lightweight top with 1mm body, UltraStretch 1mm top sleeve, and UltraStretch 0.5mm under sleeve. Front quarter-zip makes it easy to put on and take off. * Flatlock seams for comfort, super light Nylon 2 front to prevent over-stretching and filling up with water. * Ultrastretch sleeves and back make for great performance and easy on and off. * Elastic cord side cinch and front loop to tie to boardshorts to secure top from riding up. * Contoured sleeve design for maximum performance and comfort. 0.5mm soft Titanium lined collar.