The Fempro Armour can go inside crop singlet and is a breathable baselayer designed to be worn under your jersey for low-profile coverage or can be worn inside a jacket etc. When buying the armour with crop singlet option the armour can be easily removed as needed. The armour is design to increases your impact protection, the fabric of the crop singlet is breathable it is a snug fit and secure—the armour softens to conform to your body as it is warmed by your own heat—offering minimal restrictions and maximum benefit. Definitely recommend this product if you care about protecting your upper body while Mountain Biking or any sport.