The main difference between adhesives and sealants is that sealants generally have lower strength and higher elongation than adhesives. Since the primary function of a sealant is to seal assemblies and joints, sealants must have sufficient adhesion to substrates and resistance to environmental conditions to remain bonded for the required life of the assembly. When sealants are used between substrates that have different thermal coefficients of expansion or different elongation under load, they must have sufficient flexibility and elongation. Sealants usually contain an inert filler and usually contain an elastomer to provide the required flexibility and elongation. They usually have a pasty consistency to fill in the gaps between substrates. Low shrinkage after application is often required. Many adhesive technologies can be used in sealants.