Xcel's Xcelerator 1/0.5MM Long Sleeve Wetsuit Jacket is constructed of 1mm of Superstretch neoprene in the back, 1mm of Ultrastretch neoprene in the upper sleeves &. 5mm of Ultrastretch in the lower sleeves. The Long Sleeve 1/.5mm Xcelerator Wetsuit Top also has Flatlock seams because Xcel doesn't want you chafing up, bro!