A Mylar stencil remains useful when its openings are clean and the film lies flat. Dried paint along an edge can change the printed image. A crease can create space for paint to run underneath.
Clean for the paint you used
Follow the paint and material manufacturer's guidance for a suitable cleaning product. Water, alcohol and solvents are not interchangeable for every paint and film combination. Test on a small corner before treating the whole stencil.
Remove residue when appropriate for the paint. Scraping off a thick cured layer requires more force and can damage fine parts.
Support narrow connections
Place the film on a flat surface and work carefully around small letters and internal shapes. Do not pull a narrow bridge to release paint. A torn piece can no longer hold its intended position in the next print.
Dry the sheet flat
Store the stencil only when clean and dry. Keep it flat between suitable protective layers and avoid sharp folds or concentrated pressure. Stack stencils so fine openings do not catch on one another.
Inspect the edges before reuse
Check openings, bridges and alignment points. Place the stencil on the substrate to see whether it still sits flat. Recutting a sheet can be more practical than repeatedly repairing a damaged detail.
For a new version, read about designing reusable stencils. See Mylar film for material properties.