When making resin coasters, it is best to use casting resin. This type of resin is perfect for pouring into molds as it has a thinner consistency and will reach all those corners and cavities in a mold. Bubbles can also escape more easily, where you can then get rid of them. Casting resin also cures harder, so you will have a nice and firm coaster that will keep its shape. You can also decide to use a special heat-resistant resin for coasters.