Polyester vs Polypropylene Capacitors: Which One?
Polyester vs polypropylene capacitors comes down to one trade-off. Polyester is the cheap, compact, general-purpose film. Polypropylene is the low-loss, tight-tolerance film for fast work. I reach for polyester in coupling, blocking, and bypass spots where a few percent of drift is fine. I reach for polypropylene in crossovers, snubbers, and timing, where low loss and a tight spec change the result. Both are film types, so both walk all over electrolytics on stability.
Last updated: August 13, 2026 — rewrote as a head-to-head with a spec table and a plain verdict, added a bench workflow, an audio section, and fresh sourcing.
Polyester vs Polypropylene Capacitors at a Glance
Both wrap a thin plastic dielectric between metal layers. The plastic is the whole story. Polyester uses PET, the stuff sold as Mylar. Polypropylene uses a PP film with a lower dielectric constant, and that one number ripples out into loss, size, and price.
| Property | Polyester (PET / Mylar) | Polypropylene (PP) |
|---|---|---|
| Dielectric constant | ~3.2 | ~2.2 |
| Typical tolerance | ±5% to ±10% | ±1% to ±5% |
| Dissipation factor at 1 kHz | ~0.5% to 1% | ~0.02% to 0.05% |
| Max operating temp | up to 125°C | ~85°C to 105°C |
| Common voltage range | 50 V to 630 V | 100 V to 2 kV |
| Size for the same value | smaller | larger |
| Relative cost | lower | higher |
Neither wins outright. They just chase different jobs.
What Polyester Capacitors Do Best
Polyester earns its keep on the dull, high-volume parts of a board. Grab it when the value matters more than the last fraction of a percent.
- Coupling and decoupling between stages, where a 5% part is plenty.
- DC blocking in series, stripping an offset off an AC signal.
- General bypass, cheap and small across most control gear.
- Hotter corners, since PET rides up to 125°C with derating.
The weakness is loss. Polyester runs a dissipation factor ten to twenty times worse than PP, and inside a filter that shows up as heat and a mushy response. Before you assume a loose 10% part is fine, ask whether does capacitance tolerance matter here. In a timing loop it absolutely does. In a coupling cap, honestly, it rarely bites you.
What Polypropylene Capacitors Do Best
Polypropylene is the specialist. You pay more, you give up space, so you only call it in when its numbers earn their seat.
- Low-loss AC paths, because that tiny dissipation factor barely warms the part.
- Fast edges and high dV/dt, so it lands in snubbers and switch-mode supplies.
- Precision filters and timing, since a ±1% part holds steady over heat and years.
- High voltage, with 630 V, 1 kV, even 2 kV bodies being routine.
Any time real current runs through the cap at speed, I pick PP. A lossy film capacitor in that seat cooks itself. This one shrugs it off. The tax is bulk. For the same value and voltage, expect a PP body to dwarf its PET twin.
How I Choose on the Bench
When the BOM just says “film” and I have to decide, here is the ten-second sort I run.
- Does AC current flow through it fast? Yes means polypropylene. Snubber, crossover, resonant tank.
- Does it set a frequency or time constant? Yes, PP again, for the tolerance.
- Is it only passing or blocking a signal? Then polyester, smaller and cheaper.
- Will it run above 105°C? Polyester takes heat better, so lean there.
- Is space or budget the binding limit? Polyester wins both.
That is the whole thing. Value-driven and hot, go PET. Loss-driven, fast, or precise, go PP. When you truly cannot decide, over-spec to polypropylene. It rarely hurts the circuit. Only your wallet complains.
Are Polypropylene Capacitors Better for Audio?
Mostly yes, and here is the honest cut. PP owns the lowest dissipation factor of the common films, so it is the classic pick for signal paths and speaker crossovers. Less loss means less energy smeared into heat.
Do not oversell it, though. In a low-current coupling spot, the gap over a good polyester is tiny, and loads of respected gear uses PET there to save room. Where PP genuinely pulls ahead is the crossover, where speaker current pours through the cap and loss turns into measurable heat. Even so, any film runs about twenty times lower loss than a bipolar electrolytic at audio frequency. If you want the backstory on why electrolytics fade, I dug into how long electrolytics really last elsewhere.
Frequently Asked Questions
Can I swap a polyester capacitor for a polypropylene one?
Usually, yes. If the value, voltage, and footprint fit, the circuit only improves, since PP beats PET on loss and stability. Just confirm the bigger body still lands on the pads.
Which one has lower loss?
Polypropylene, and it is not close. Its dissipation factor sits near 0.02% to 0.05% at 1 kHz. Polyester runs closer to 0.5% to 1%, roughly a tenfold gap.
Which handles higher temperatures?
Polyester. PET works up to about 125°C with derating, while standard PP tops out near 85°C to 105°C. Heat is one of the few rounds polyester clearly takes.
Why is polypropylene bigger and pricier?
Its dielectric constant is lower, about 2.2 against 3.2. You need more film area for the same value, which grows the body and the cost.
Are both types non-polarized?
Yes. Both are film capacitors, so neither carries a polarity mark. Drop either one in any direction, unlike an electrolytic.
Related Reading
Bottom Line
The polyester vs polypropylene capacitors call is a two-line rule. Pick polyester when size, cost, or heat drive the design and a few percent of tolerance is fine. Pick polypropylene when loss, precision, speed, or high voltage drive it, and you can spare the room. Either film beats an electrolytic in the signal path, so any film is a step up.
