Iron-on patches. The sticky side contains polyethylene adhesive. 

Application: Iron-on patches are suitable as an interesting addition to jackets, shirts or pants. They are used primarily where it is necessary to strengthen or to patch up some clothing (knees, elbows etc.).

Instructions for use : Remove the protective film from the bottom side. Lay it with the shiny side on the fabric (do not use synthetic fabrics). Do not use steam. Iron it over piece of cloth. Iron with higher pressure for 15 to 20 seconds. Then let the cloth cool for 15 minutes. 
We recommend to sew it on, so it won't peel off when washing.