There are several different methods for making stencils to use to paint designs onto a bicycle frame, but one way involves using frisket film. Frisket film is used in painting and airbrushing and is a clear flexible plastic film with a light sticky backing, making it perfect for bike stencil application.
Draw the design you want to make a stencil for on a sheet of paper. Use a pencil at first, then retrace later with a black pen. Wrap the paper onto the bike frame to make sure the size and shape is correct.
Tape the paper with the design to your workspace or light box. Lay a sheet of frisket film onto the design. Trace the design on the frisket film with a fine point felt pen. Remove the film and store the paper with the original design in a safe place for later.
Lay the frisket film out on a surface you can cut on. Cut out your design making a negative space stencil to use for painting. Peel the backing on the frisket film when ready to use and apply to the bicycle frame. Paint, then remove.