Electrolytic & film capacitors

Electrolytic capacitors:
Electrolytic capacitors have an insulator in the form of a substance or mixture (usually liquid with dissolved salt) that has a high concentration of free ions and is able to conduct current. This achieves a higher capacitance (ability to store electrical charge in a component) compared to other capacitors.

There are three classes of electrolytic capacitors: aluminium, tantalum and niobium electrolytic capacitors.

Film capacitors:
Film capacitors are one of the most common types of capacitors and encompass an extensive range, where the main difference is the material used as the insulator (polyester, polystyrene, polypropylene polycarbonate, metallised paper or Teflon).

Ceramic capacitors: 
Ceramic capacitors are also very common. Their capacitance varies in line with voltage and temperature, making them difficult to use in many applications. MLCC “Multi Layer Ceramic Capacitor” is a type of ceramic that has higher capacitance than the standard version. Common temperature classes include X7R and X8L. The most common safety-rated types are X1/Y1 and X2. 

How do you know what you need?
Important parameters include how is it going to be used, what features are required and whether there are any other constraints (e.g. size limitations).

Electrolytic capacitors:
+ Handle greater capacitance (the ability to store energy)
+ Affordable capacitor
- Service life is generally slightly shorter
- Less potential to influence the shape, basically only available round

Film capacitors:
+ Handle higher voltages
+ Can be made slightly thinner as the film can be compressed
+ More design options (e.g. oval, round, rectangular)
+ Long service life
+ High temperature tolerance
- Handles lower capacitance

Ceramic capacitors: 
+ Handle larger voltages 
+ Small and cheap 
+ Available in safety classes X1/Y1 and X2 
- Capacitance that fluctuates with temperature and voltage