In chemistry and common usage, a filter is device (usually a membrane or layer) that is designed to block certain objects or substances whilst 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, etc..

See also

Filters for various substances:

• Filter (water)
• Filter (air)

Filters for specific applications:

• Pneumatic filter
• Coffee filter
• Filter mask

Filters by various methods:

• Filter paper
• Media filter
• Screen filter
• Disk filter
• Sand separator
• Slow sand filter bed
• Electrostatic dust filter

Related devices and concepts:

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