Do I need a mold release, and which one?
It depends on the materials in contact. Here are some basic rules.
- Casting urethane/resin INTO a silicone mold: usually no release needed, silicone is naturally non-stick. (Exception: some resins benefit from a light release like Ease Release 200 to extend mold life.)
- Casting silicone INTO a silicone mold, or silicone against silicone: you must use a release or the two will fuse. A dedicated silicone-on-silicone release is required here. Ease Release 200 or 205 is recommended.
- Anything against a porous master (plaster, wood, stone, concrete): seal it first (Superseal), then apply release.
- Urethane over any master: always release. Universal Mold Release recommended.
- Urethane into a urethane or rigid mold: always release. Universal Mold Release recommended.
Aerosol release tips: Use the "spray-brush-spray" method. Apply a light mist coating of release, brush over the surface wth a dry brush, then apply another light mist coating. Pooled release leaves texture and can cause surface defects. For skin-contact parts, residual release should be washed off (warm water + dish soap; an isopropyl-alcohol wipe further reduces residue).
Learning Center:
Full guide: Choosing and Using Release Agents and Sealers