Short answer: a casting or art epoxy rated for ¼–½" pours (coasters are usually 6–10 mm thick) with a UV stabilizer; coating/tabletop epoxy works for thin layers but may overheat in a full-depth mold.
| If you want… | Look for |
|---|---|
| Clear coasters in silicone molds | Art/casting epoxy rated ≥ your coaster depth |
| Coated wood or tile coasters | Tabletop/coating epoxy, ⅛" flood coat |
| Hot mugs | Check the maker's published heat resistance for the cured resin; most epoxies soften with heat |
| Lots of color and inclusions | Longer working time; mica or resin pigment (ratio calculator) |
Work out how much to mix with the coaster calculator (a 100 mm × 8 mm coaster holds about 63 ml).
Most cured epoxies soften with heat; some are marketed with higher heat resistance. Check the maker's spec and add cork or felt backing.
Usually 6–10 mm; pour within your resin's maximum depth.
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More tools: resin calculator · mix ratio by weight · cure time · mold volume · tabletop coating · pouring too thick