Alpinestars Nucleon KR-CELLi Back Protector The Alpinestars Nucleon KR-CELLi Back Protector, constructed of a polymeric material blend, features a triple segmented back shell plate which creates the perfect balance between energy absorption and force dispersion. The ergonomic design of the Nucleon KR-CELLi, in tandem with the horizontal flexion grooves, allows it to contour to the natural curve of the back to provide a fit that molds to a variety of riding positions. Features: Triple segmented back shell plate constructed of a polymeric material blend Unique cell micro-structure designed for advanced energy absorption, adaptivity, maximum breathability and air flow Ergonomic protection plate contours to the natural curve of the back Horizontal flexion groves for an adaptive fit in different riding position Airmesh on the body side of the protector offers maximum breathability CE Level 1 protection Fitment: Women's Stella Jackets: 36-38 or XS-SM: Small Nucleon 40-50 or MD-3XL: Medium Nucleon Men's Jacket: 44-50 or XS-MD: Medium Nucleon 52-64 or LG-4XL: Large Nucleon