The main difference between adhesives and sealants is that sealants typically have lower strength and higher elongation than 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. Wheel and roller applicators provide a variety of pattern options, but may require frequent cleaning if the adhesive cures on it. These applicators apply hot melt adhesive from the top, the bottom or side, and patterns can be tailored to meet specific production needs.