What is Polyester Capacitor : Working & Its Applications

Capacitors working frequently get restricted because of different losses like surge or leakage. When leakage loss can be decreased by appropriate insulation using a ceramic or an epoxy coating, damage can be avoided because of short circuits. Depending on the dielectric type used, the capacitors like metal film are either of polyester or polypropylene type. This article discusses an overview of a polyester capacitor & its working.

What is Polyester Capacitor?

The polyester capacitor is designed with two metal plates where the polyester film is arranged between them; otherwise, a metalized film can be placed over the insulator. The polyester capacitor capacitance ranges from 1nF -15µF and works from 50 to 1500V. The tolerance ranges of the polyester capacitors are 5%, 10% & 20% and the polyester capacitor temperature coefficient is high.

The isolation resistance of these capacitors is high, so these are the best choices for storage or coupling applications. These capacitors are extremely heat resistant so they can work close to 150 °C temperatures. The polyester capacitor symbol is shown below.

Polyester Capacitor with Symbol
Polyester Capacitor with Symbol

As compared to other types, the capacitance of polyester capacitors has high for each unit volume that means high capacitance can fit into a small capacitor. This feature, together with their relatively low price makes polyester capacitors a widely used, popular, and cheap capacitor. They are used in moderately high-frequency circuits and audio and oscillator circuits.

Polyester Capacitor Construction

Polyester capacitor uses two metal foil pieces like electrodes which are sandwiched within a very thin insulating medium & rolled into a cylindrical otherwise smooth cylindrical core. The polyester capacitors are available in two types like a metalized film & a foil version. These capacitors are designed with metal & polyester layers otherwise Mylar dielectric for making capacitance values in a wide range.

The dielectric constant of Polyester is high & it is capable to distribute a product with less cost in a small design. The shield of the capacitor is made with an epoxy resin capsule which is coated firmly in the region of the capacitor.

Polyester Capacitor Construction
Polyester Capacitor Construction

The higher face of the epoxy shell includes the voltage & capacitance that is printed on it. It includes a pair of connecting terminals at both faces.

The dielectric material used in this capacitor like Polyester is most extensively used so that the construction of this capacitor will be reduced. These capacitors have excellent self-healing properties & are comparatively economical.

A polyester capacitor with a high temperature will dissipate huge power, so this feature will make the capacitor inappropriate for the applications of high current & frequency. In addition, polyester material shows a major change in capacitance up to 5% when the temperature comes close to high or low-temperature limits. Because of this feature, polyester material is inappropriate for designing precision capacitors.

Types of Polyester Capacitor

Polyester capacitors are classified into three types based on their adjustability like fixed, trimmer variable & trimmer capacitors. Based on the media, these are classified as gas, inorganic solid, organic solid, electrolytic, liquid & composite.

Types of Polyester Capacitor
Types of Polyester Capacitor
  • Gas capacitors comprise vacuum, air, gas-filled
  • Inorganic type includes mica, glass glaze, ceramic
  • Organic type includes paper dielectric & organic film
  • Electrolytic dielectric type includes niobium electrolytic, aluminum electrolytic & tantalum electrolytic
  • Liquid dielectric type includes liquid & various organic oily
  • Composite dielectric type includes the capacitors which are made with an organic, inorganic solid compound, organic solid & inorganic solid compound.

Similar to other capacitors, these capacitors have several tiny classifications like the common CL11 & CL21. But the main dissimilarity is that the inside wall of the capacitor like CL21 utilizes metallization technology. As compared to CL11, Cl22 volume is much lesser; however, the overall act is not as superior as CL11.


The main properties of polyester capacitors include the following.

Leaded Versions

These capacitors are simply accessible in leaded versions instead of surface-mount packages.

High Dielectric Strength

The polyester dielectric utilized within these capacitors also called PET that provides maximum dielectric power. So the capacitors with high voltages can be designed fairly small.


The tolerance of many kinds of polyester film capacitors simply has 5% or 10%, so that is adequate for several applications, however. At present, capacitors with better tolerances are available at a low cost.

Operating Temperature

As a consequence of the polyester dielectric properties, these types of capacitors frequently operate at 125°C of temperatures, even though through a voltage de-rating.

Equivalent Series Resistance or ESR

The equivalent series resistance of polyester capacitors is low level.

High dV/dt

The dielectric & construction of polyester, PET capacitors are used in different applications wherever sharp; spikes of quick rise time are there when they contain high dV/dt.

How to Check Polyester Capacitor?

Once a polyester capacitor is connected within an active circuit, then charge begins to supply within the capacitor & once the capacitor gets charged then it will not accept any charge. There are several techniques to test a Capacitor to check its functioning. Some of the techniques include the following.

  • Using Multimeter through Setting of Capacitance
  • Using AVO Meter or Analog Multimeter
  • Using Multimeter without Setting of Capacitance
  • Using a simple Voltmeter
  • Capacitor testing through the Time Constant measurement
  • Capacitor Leads Shorting

Features & Advantages

In electronic produces, a polyester capacitor is a fundamental and essential component and polyester is used as the medium. The dielectric constant of type of capacitor is high, tiny in size has good stability & huge capacity. They are appropriate for bypass capacitors & the ratios like volume-to-volume & price-capacity are better as compared to electrolytic &ceramic type capacitors.

Characteristics/ Features of polyester capacitor include the following

  • Less Weight
  • Tiny Size
  • Stability is Good
  • High Reliability
  • The welding of lead wire can be done directly toward the electrode with less loss
  • Structure is Sensitive
  • Encapsulated through Polyester Film & Epoxy Resin

The advantages of Polyester capacitors include the following.

  • Accuracy
  • Better Environmental Adaptability
  • Loss Angle
  • Reliability
  • Insulation Resistance
  • Temperature Characteristics

Polyester Capacitor Applications

Polyester capacitors are also called PET/ Mylar which is utilized in several areas where leaded capacitors can be accommodated. Some polyester film capacitor uses include the following.

  • This capacitor is used where maximum levels of peak current need to handle
  • Used in different low-frequency pulsating & DC circuits
  • Used for filtering wherever high levels of tolerance are not necessary.
  • Used in the applications of coupling, decoupling & blocking of DC
  • Used in power supplies wherever the levels of the extremely high capacitance of electrolytic capacitors are not required.
  • Used in the applications of audio
  • These capacitors are frequently regarded as good general-purpose capacitors. Although they cannot provide a high range of tolerance as well as accuracy, they can be used in several other applications which provide good volumetric capacitance levels.
  • Used in noise suppression circuits.

Difference between Ceramic and Polyester Capacitor

  • The dielectric used in the film capacitor is typically polyester otherwise polymer film.
  • As compared to film capacitors, ceramic capacitors are fairly non-linear within their voltage & frequency responses.
  • Ceramic capacitors tend to act as microphones, so picking up ambient noise & changing the voltage beyond them consequently.
  • For smaller values, ceramic capacitors are used commonly whereas for larger values polyester capacitors are used.
  • In these capacitors, both ceramic & film caps are non-polarized
  • Polyester capacitor delivers an inexpensive product within a little outline & operates at 125°C of temperatures.
  • Polyester capacitors are frequently regarded as high-quality general-purpose capacitors. Even though they cannot offer a high range of accuracy & tolerance but they offer good ranges of volumetric capacitance.
  • In the fixed value capacitor like a ceramic capacitor, the ceramic material works like the dielectric. This capacitor is designed through two or above alternating ceramic layers & a metal layer works like the electrodes. The ceramic material composition describes the electrical performance & its applications.
  • For the applications of the resonant circuits, ceramic capacitor offers high stability & low losses
  • For the applications of bypass, buffer & coupling, these capacitors offer high volumetric efficiency.
  • Ceramic type capacitors are MLCCs (multilayer ceramic capacitors), which are mostly used in electronic equipment that integrate around one trillion pieces each year.

Thus, this is all about an overview of one kind of film capacitor like a polyester capacitor. This is that depends on the type of dielectric material. The commonly used capacitors are Polyester & Polypropylene. The polyester capacitor is also called polyester film and the dielectric material used in this is made with a polymer known as PET or polyethylene terephthalate. So this is the main reason to call this capacitor a PET Film Capacitor. As compared to other manufacturers, the leading manufacturer of this capacitor is “Hostaphan”. Sometimes, Polyester Capacitor is also known as a Mylar Capacitor. Here is a question for you, what are the different types of film capacitors?