The best nipple covers available today are the Bye Bra stick on nipple covers. 
They are made from a Henkel adhesive and are tested by SGS. 
The stick on nipple covers are comprised of an adhesive back side with a soft front side. These flower-shaped dark silk stick on nipple covers are perfect for daily wear. 
They conceal nipple protrusion, and will protect your nipples, regardless of whether or not you wear a bra. 
The nipple covers are invisible under a bikini, dress, T-shirt or evening dress, nobody will know you are wearing them.
 
size: one size, 8 cm wide
composition: paper release liner 50%, non woven polyester30%,polymetric adhesive 20%