Wood is made up of cells that contain lignin and cellulose. When wood absorbs water, the cells can become damaged or change shape due to warping, bowing, and cupping. To prevent water damage, wood is often treated with resin, which is made from tree sap or synthetic materials. The treatment process involves exposing wood to resin under pressure or heat so the resin penetrates the cells. Generally, resin seals the cells and prevents water absorption, protecting the wood from long-term damage.