DIY Coaster Silicone Mold, Pack of 4 Resin Molds for Casting Eco-Friendly Sturdy Hexagon Square Round Mold Bottom Bracket for Casting with Resin,Concrete,Cement. 4.7 out of 5 stars. 3,275. $8.99. $8. . 99. In this kit are 4 resin molds in 3 geometric shapes -- great for coasters, holders, and more.