In chemistry, a suspension is a heterogeneous mixture in which one substance is dispersed throughout a substance in another phase, and in which the particles of the first substance are between 0.00002 and 0.00004 of an inch in diameter. In order to be a suspension rather than a colloid, the mixture must be capable of sedimentation if allowed to stand. Most suspensions are comprised of solid particles suspended in a liquid, such as paint, blood or muddy water, but they can also consist of liquid particles suspended within a gas, such as an aerosol spray.
The particles contained in a suspension are usually large enough to deflect light and cause the mixture to appear opaque or cloudy. A suspension is also filterable, which is another property that distinguishes it from a colloid.
When a suspension consists of a liquid or solid substance suspended in a gas, it is called an aerosol or particulate. Dust and soot suspended in the atmosphere are examples of particulates. Neither a suspension nor a colloid, however, can be comprised of one gaseous substance suspended in another gas. This is because the particles of gases are small enough to always form a solution when mixed.
Because suspensions will eventually separate, certain consumer products that are suspensions have usable shelf-life restrictions, or they require vigorous physical remixing before use, such as house paint. The ability of a suspension to resist changes of separation over time is referred to as its dispersion stability.