A sealant may be viscous material that has little or no flow characteristics and stay where they are applied or thin and runny so as to allow it to penetrate the substrate by means of capillary action. Anaerobic acrylic sealants generally referred to as impregnants are the most desirable as they are required to cure in the absence of air, unlike surface sealants that require air as part of the cure mechanism that changes state to become solid, once applied, and is used to prevent the penetration of air, gas, noise, dust, fire, smoke or liquid from one location through a barrier into another. Typically, sealants are used to close small openings that are difficult to shut with other materials, such as concrete, drywall, etc. Desirable properties of sealants include insolubility, corrosion resistance, and adhesion. Uses of sealants vary widely and sealants are used in many industries, for example, construction, automotive and aerospace industries.

The main difference between adhesives and sealants is that sealants typically have lower strength and higher elongation than do adhesives. Since the main objective of a sealant is to seal assemblies and joints, sealants need to have sufficient adhesion to the substrates and resistance to environmental conditions to remain bonded over the required life of the assembly. When sealants are used between substrates having different thermal coefficients of expansion or differing elongation under stress, they need to have adequate flexibility and elongation. Sealants generally contain inert filler material and are usually formulated with an elastomer to give the required flexibility and elongation. They usually have a paste consistency to allow filling of gaps between substrates. Low shrinkage after application is often required. Many adhesive technologies can be formulated into sealants.