High quality masking paper.
High quality airbrush paper. Special for modeling. Transparent PVC film with acrylic adhesive. Low adherence, zero residue, especially for masking scale models, works really good over glossy or matt surface. Cut to desired size with a sharp blade and place the piece of sheet over the model to be airbrushed. Spray thin coats of paint, not trying to cover with the first coat, avoiding puddling of paint on the edges. Once dry, remove the mask. The result is a clean and sharp paint edge. Drawing on the back side of the sheet with a pencil, you can make the stencil you need for your diorama or model.