In chemistry and common usage, a filter is a device (usually a membrane or layer) that is designed to block certain objects or substances while letting others through. Filters are often used to remove harmful substances from air or water, for example to remove air pollution, to make water drinkable, to prepare coffee. In domestic food and drink preparation where bulk solids are removed from liquids, this is often called a strainer.

Filtrate is the liquid produced after filtering a suspension of a solid in a liquid.

See also

• Filter (water)
• Filter (air)
• Filter (oil)

Filters for specific applications:

• Pneumatic filter
• Coffee filter
• Filter mask

Filters by various methods:

• Disk filter
• Electrostatic dust filter
• Paper filter
• Media filter
• Membrane filter
• Sand separator
• Screen filter
• Slow sand filter

Related devices and concepts:

• Activated carbon
• Non-Filter (trade name).
• Gas mask
• Sieve
• Colander
• Reverse osmosis
• Filter feeder
• Filter binding assay

Filters