When sourcing security void material, you must prioritize tamper-evident performance and substrate compatibility. Key specs include the transfer type (Total Transfer, Partial Transfer, or Non-Transfer), film thickness (typically 25-50 microns), and adhesive strength. Ensure the material uses high-contrast 'VOID' messaging or custom patterns that appear instantly upon peeling. For high-end applications, verify the surface tension (dyne level) to ensure it is compatible with your specific printing inks or thermal transfer ribbons.