Many factors enter into the selection of a sealant, not the least of which are final application and cost. Minor changes in composition can cause major changes in properties.

Thermal factors include temperature extremes and variations, and cyclic frequency of the variations.

Chemical resistance to any specific agent can be obtained by proper formulation.

Weatherability is important for sealants exposed to outdoor service conditions.

Mechanical properties of importance include strength, elongation, compressibility, modulus of elasticity, tear resistance, and fatigue resistance.

Abrasion resistance is usually highest among the flexible sealants, especially urethanes and neoprenes.

Adhesion depends largely on the interaction between the sealant and the surface to which it is applied.

Electrical characteristics vary widely among sealants. Proper formulation can to a large extent control dielectric strength, dielectric constant, volume and surface resistivities, and dissipation factor.

Flameproof sealants are available for hazardous locations.

Nontoxic formulations are available for equipment in contact with foodstuffs.

Repairability is important in applications where the sealant may be broken during service. Some sealants, especially the nonhardening formulations, are easily replaced.

Production procedures are important, because improperly applied sealants often fail in service.