Cut a nice strip of a can.

Get your stencil for your necklace and draw around it with a compass so that you lightly draw a line

Then cut that out

Get your foam and draw around the coke stencil. Cut this out too

Then pucnch a hole where you want your jump rings to be. Make sure it is on the same place as the foam

Then glue the tho together and put your jump rings through