The short answer
PPA melts higher, keeps its stiffness when hot and absorbs much less moisture, so it suits hot, wet and dimension-critical parts. PA66 is tougher, easier to mold and lower cost, so it remains the default for parts that run cooler. Both are usually used glass-filled.
PPA is the usual step up when glass-filled PA66 parts creep, lose stiffness or change size in hot or humid service. It is also a common answer when PA66 is short or on allocation and the part has heat margin to protect.
Side by side
| Property | PPA | Nylon 66 (PA66) |
|---|---|---|
| Family | Semi-aromatic polyamide | Aliphatic polyamide (nylon) |
| Melting point | ~290–325°C (by type) | ~260–265°C |
| Glass transition (dry) | ~100–140°C | ~60–70°C (drops as it absorbs water) |
| Heat deflection, 1.8 MPa (30–33% glass) | ~270–290°C | ~245–255°C |
| Stiffness above 100°C | Holds more | Drops more |
| Moisture absorption | Low; roughly a third to half of PA66 | Higher; size and stiffness change with humidity |
| Toughness | Lower; weld lines need care | Higher |
| Melt temperature | ~320–340°C | ~280–300°C |
| Mold temperature | Often ~135–165°C; some grades ~85–100°C | ~70–95°C |
| Relative cost | Higher | Lower |
| Typical uses | Engine-area parts, coolant housings, reflow connectors | Brackets, housings, clips, fan shrouds, connectors |
Typical values for glass-filled molding grades unless noted; PPA types and grades vary widely, so compare specific data sheets.
Choose PPA when
- Parts run continuously above about 120°C
- Stiffness must hold when hot and wet
- Size must stay steady in humid service
- Hot coolant, fuel or lead-free reflow is involved
Choose PA66 when
- Service temperatures are moderate
- Toughness and weld-line strength matter
- Standard water-heated molds are all you have
- Cost is a key driver
Moving from PA66 to PPA
- Confirm the need: heat, moisture or creep, not a processing problem.
- Check the mold: mold temperature capability, steel and venting for higher melt temperatures.
- Pick the grade type: hot-mold or water-mold PPA, and the glass level that matches your part.
- Dry well: PPA is sensitive to moisture at molding.
- Watch weld lines and snap fits: PPA is less forgiving than PA66.
- Trial and test the part at its real service temperature.
See also PA66 shortage alternatives, nylon 6 vs. nylon 66 and parts softening under heat.
Grades we source
We source glass-filled PPA and PA66, including heat-stabilized and hydrolysis-resistant grades, from one gaylord up, with a COA on every lot, tested to ASTM or ISO methods. See PPA and glass-filled nylon.
Common questions
What is PPA?
Polyphthalamide, a semi-aromatic polyamide. It is part of the nylon family but melts higher, stays stiffer when hot and absorbs less moisture than nylon 66. Most molding grades are glass-filled.
Is PPA better than nylon 66?
For hot, wet or dimension-critical parts, yes. PPA keeps more of its stiffness and strength above 100°C and changes size less with humidity. For parts that run cooler, PA66 is tougher, easier to mold and costs less.
Why is PPA more expensive than PA66?
It is made in much lower volumes, often with specialty diamines, and it needs hotter processing. Most buyers use it only where PA66 runs out of heat or moisture resistance.
Can PPA run in a PA66 mold?
Sometimes, but plan for changes. Many PPA grades need much hotter molds (often oil-heated) to crystallize fully, and higher melt temperatures. Some grades are designed to mold at water-heated temperatures. Shrinkage of glass-filled grades is similar but not identical, so trial and measure.
Does PPA need drying?
Yes. Like PA66 it must be dried before molding, and many PPA grades call for a lower moisture limit. Follow the data sheet and use a desiccant dryer.
What parts use PPA instead of PA66?
Under-hood parts near the engine, coolant and thermostat housings, fuel system parts, and electrical connectors that see lead-free solder reflow.
Tell us the grade you run now
A polymer chemist reviews every request, then matches your grade or finds a qualified equivalent and prices it.
What to send for an accurate quote
- The grade name, from any supplier, or a data sheet
- Color (natural, black or a custom match)
- Fill type and percentage, if any
- Melt flow, if you know it
- Quantity for this order and what you use in a year
- Ship-to city and state or province