Capacitor Selection Guide

Capacitors are one of the most common components in electronic devices, but not all capacitors are made equal. The capacitor model you were taught were two metal plates are very near to each other and use some dielectric material in the middle might not be as accurate as you think.

Also, the ideal capacitor of your schematics in your ideal world of the non-existence is not an accurate description of the reality, where things (physical devices) have size, age, cost, temperature-dependant behavior, etc.

This post is a short descriptions of the pros, cons and dangers of different capacitor kinds you can use as a hint for your decisions when you work on your designs.

First of all, there’s always a Wikipedia article that explains anything you would like to, but it’s not always done the way you would. The classification image is, in this case, a great resource to start if you want. Find it in this link:

You can read a lot about the internal structure and about how do all those kind of capacitors work in the inside, but this guide is mostly about the pros and the cons and what you should check in the first look.

There are other kinds that are not mentioned here but they are not as common as these. If you want to add something or you see something wrong, please contact (contact info at the bottom of the page) and this list will be updated.

Electrolytic capacitors

Electrolytic capacitors are mostly crap. But they have some uses though because they have a very high capacitance.

You probably have seen some of this cylinder-looking motherfuckers here and there. They are fairly common. They come also in other shapes but those cylinders are easy to spot.





Specific notes about Tantalum capacitors:

Ceramic (multi-layer)4 capacitors

Ceramic capacitors are one of the best in business and they are the most popular, but have to be chosen carefully.



They come in two classes depending on their dielectric type: Class I and Class II, that we have to describe separately because they are quite different.

Class I

The first class are the best ones, period.

There are different kinds depending on their dielectric material: NPO, COG and more, but they all are similar.




Class II

The class II groups many different dielectrics. They are described by a three character string: X5R, X7R, Y5V…

For a better understanding of the identification, check the wikipedia page on the topic or read any datasheet5. Compare their stability with the ones on the class I, and you’ll see.




Plastic-film capacitors

Plastic film capacitors are made using plastic as a dielectric and they come in many flavors, as much as different plastics we have available. The most used ones are Polypropylene (PP) and Polyester (PET) and, interestingly enough, they have opposite characteristics in some cases.

They are mostly made for through-hole technology.

Polyester (PET)

Polyester capacitors are very cheap and they are decent for many applications.




Polypropylene (PP)

Polypropylene capacitors are very stable and have low losses, similar to Class I ceramic capacitors, so they are suitable for the same kind of applications but they can handle higher currents.




EXTRA: Line-rated capacitors

Line-rated capacitors or mains-rated capacitors are special capacitors (normally PP or ceramic) for cases where they need to be connected to the power supply mains. They need special safety classification to protect people from danger.

They have a fuse-like capability so if they get burn they lose some capacitance but they are never short-circuited to avoid fires and electric shocks.

They mostly come in two different classes, X and Y, each one for a different application.

If you need to interact with the mains, please, use these and no other.


Nowadays technology is good enough to let you use ceramic capacitors for almost any electronics design or application. For those cases where a very high capacitance is needed, you have no other choice than going for electrolytic.

In the case you are using Class II ceramic capacitors you have to be extremely careful with your selection and check the temperature dependency.

In through-hole technology, Polyester (PET) caps can be a cheap and decent choice for simple applications, while polypropylene plastic film (PP) capacitors can be useful for all other applications where higher capabilities of current or frequency handling are needed.

For extremely high capacitance applications where no other option is valid electrolytic capacitors are the only option you have. If you need them to be small, tantalum ones are your last resort.

If you are working with the mains you MUST go for line-rated versions.

  1. If they are small they are like a firecracker, but if they are large they can be really dangerous. The classic cylinder looking ones have like a cross on the top making the enclosure able to puff up to reduce the chances of explosion, but they blow up anyway if you try hard enough, and even if they don’t they don’t work anymore so your circuit is compromised anyway.↩︎

  2. The ESR is the Equivalent series resistance of the capacitors. Ideal capacitors don’t exist so we have to be satisfied with the crap we have. Non-ideal capacitors are approximated in circuits with a resistor, a capacitor and an inductor in series. The ESR corresponds to that resistor, which represents the ohmic losses in the device at a certain frequency.↩︎

  3. Fun fact: At time of writing, the Panasonic I mention in the point above is out of stock in the distributor where I found it.↩︎

  4. They are called ceramic and multi-layer interchangeably because they are made by multiple layers of ceramic material.↩︎

  5. Like this one from Samsung Electro-Mechanics.↩︎