The main purpose of a sealant is to seal joints. Sealants need to be able to sufficiently adhere to the primary substrate and be resistant to environmental conditions to remain bonded for the required life of the joint. Sealants provide excellent thermal co-efficiency between two substrates allowing for the expansion and contraction of the joint under stress. Sealants tend to contain inert filler material and are usually formulated with a natural or synthetic polymer to give the required flexibility and elongation properties. As a paste-like consistency, a sealant is typically used to fill gaps between substrates.

Sealants, seal the substrate and are particularly effective in keeping moisture away from the joint in which they are used. They provide thermal and acoustical insulation and fire resistant sealants may serve as fire barriers.

Sealants have three main functions.  

1. To fill gaps between two substrates; either mechanically or aesthetically.

2. Forms a barrier through the physical properties of the sealant itself and is a reliable weather seal application to the substrate.

3. It is able to sustain its sealing properties for the expected lifetime of the sealant.