I would be happy to explain the differences between the various HEAD Radar/Rachel helmets: Radar - Unisex - Available from XS/S to XL/XXL Rachel - Women version - Softer padding in helmet - Available in XS/S and M/L - SL means Sparelens (extra glass for bad weather conditions) - 5K (new lens technology) - PHOTO - (adjusts visibility between S1 and S3 depending on weather conditions) - MIPS (an additional layer integrated in the helmet with low friction of the MIPS Brain Protection System)