We recommend using ArtResin on the exterior of drinkware and only on drink ware intended for use with cold beverages. We don't recommend using ArtResin to line the interior of drinkware. This is not a safety issue ( ArtResin is inert once cured ) but rather a temperature issue. The maximum temperature ArtResin can be exposed to is 120F / 50C. A hot beverage, like a freshly brewed coffee or tea, is far hotter than 120F / 50C and the resin can become irreparably damaged if exposed to temperatures higher than this.