Permanent.
Variable. Their capacity can be changed either manually by the operator (user) of the device, or under the influence of voltage (as in varicaps and variconds).
By the polarity of the applied voltage:
Polar - when voltage of the wrong polarity is connected, they fail.
Depending on where these components are used, there are different material options:
Paper and metal-paper are capacitors familiar to many, widespread in Soviet times, in the form of rectangular bricks with markings like "MBGCh". The appearance of this type of capacitors you can greece mobile database below. They are non-polar.
Ceramic - they are often used to filter high-frequency interference, and the relative permittivity allows for the production of multilayer components with a capacity comparable to electrolytes (expensive), and are not sensitive to polarity.
Film - common in the form of brown pads, inexpensive, used everywhere. Characterized by low leakage current, small capacity, high working voltage and insensitivity to the polarity of the applied voltage.
With an air dielectric. The best example of such an element is a tuning capacitor of a resonant circuit from a radio receiver, the capacity of such elements is small, but it is convenient to implement its change.
Electrolytics are elements in the form of barrels, they are most often installed as a filter for network pulsations in power supplies. The design and operating principle allow for a large capacity with small dimensions, but over time they can dry out, lose capacity or swell. You can see below what these products look like in good condition. A thin layer of metal oxide is used as a dielectric. If capacitors with a dielectric made of AL2O3 are used in power supplies - the so-called "aluminum electrolytes", then tantalum (Ta205 - they also belong to electrolytes) capacitors are used for work in high-frequency circuits, because they have a lower leakage current, greater resistance to external influences, unlike the previous aluminum ones.
Polymer - capable of withstanding high pulse currents and operating at low temperatures
Main technical characteristics