A sealant is a material used to fill gaps or cracks in order to prevent the passage of air, water, dust, or other substances. TAR and oakum are two common materials used as sealants. TAR is a dark, viscous liquid derived from the distillation of coal, wood, or petroleum. Oakum is a material made from hemp or jute fibers that have been treated with TAR or pitch. Both TAR and oakum are used to fill gaps and cracks in walls, roofs, and other structures, making them an effective sealant.