Seriously technical the use of Ultrasonic Tape Bonding technology reduces the need for classical stitching, making the garment lighter and softer and seam overlaps fall away, removing potential chafing points. Having said all that the thing we love most about the Quantum is it looks fantastic, it is bright but not ugly, has good arm and body length and definitely brings a new style chic to winter high viz running wear. We love stylish technology! A medium equates to a size 12.