You bench-test a PA6+30GF bracket in the shop. Flexural modulus hits 8,000 MPa — passes every load spec. Six months outdoors, that same bracket has soaked up 2% moisture and lost nearly half its stiffness. It sags under a load it once carried standing still.
That 44% modulus drop isn’t a defect. It’s chemistry. The amide groups in every polyamide chain pull water out of ambient humidity. Those water molecules plasticize the matrix and weaken the fiber-matrix bond. Flex modulus goes from 8,000 MPa dry to 4,500 MPa conditioned. If your data sheet only shows dry values, you’re designing blind for outdoor structural parts.
PPA+30GF solves the problem at the polymer level. Polyphthalamide has lower amide-group density — it absorbs under 0.5% moisture even in sustained outdoor exposure. Flex modulus holds above 10,500 MPa wet. You pay roughly 2.5x material cost but the part keeps its rated stiffness for the full service life.
I watched an OEM learn this the hard way. They ran PA6+30GF for an outdoor equipment bracket. QC passed at the press — dimensions on print, strength numbers on paper. Eighteen months in the field, every bracket had crept over 1% under sustained load. The retrofit cost wiped out the material savings five times over. PPA would have cost more on the BOM but saved the program.
Moisture Absorption and Modulus Retention
Moisture drives every other mechanical property in outdoor glass-filled nylon parts. Here’s how the three options compare:
| Property | PA6+30GF | PA66+30GF | PPA+30GF |
|---|---|---|---|
| Moisture Absorption | 1.5-2.5% | 1.0-1.8% | 0.2-0.5% |
| Flex Modulus (Dry) | 8,000 MPa | 9,000 MPa | 12,000 MPa |
| Flex Modulus (Cond.) | 4,500 MPa | 5,500 MPa | 10,500 MPa |
| HDT @ 1.8 MPa | 195°C | 240°C | 280°C |
| Creep @ 50% Load (1000h) | 0.8% | 0.5% | 0.2% |
| Cost Index | 1.0x | 1.3x | 2.5x |
PA6+30GF loses 44% of its flex modulus after moisture conditioning. PA66+30GF drops 39%. PPA+30GF loses 12.5%. For a bracket that lives outdoors and carries a constant load, that retention gap decides whether the design works.
Heat Deflection and Creep Resistance
Outdoor parts deal with more than humidity. Direct sun on a dark plastic surface can push 80°C easily. HDT at 1.8 MPa tells you where the material softens under load — PA6+30GF at 195°C, PA66+30GF at 240°C, PPA+30GF at 280°C. All three clear typical outdoor conditions. But HDT is measured dry. Moisture reduces the effective HDT of conditioned PA6 by 20-30°C. That gap matters if your part sits near asphalt in July.
Creep is where the cost difference earns its keep. At 50% of ultimate load over 1,000 hours, PA6+30GF creeps 0.8%. PA66+30GF does better at 0.5%. PPA+30GF holds at 0.2%. Four times less creep than PA6 means the geometry you designed stays where you put it. For a bracket holding a solar panel or a structural support arm, that’s the difference between a one-time installation and a service call every two years.
When to Spec Each Material
PA6+30GF works for indoor structural parts with controlled humidity and intermittent loading. If the part lives in a conditioned space and doesn’t carry sustained stress, the cost savings are real.
PA66+30GF is a modest step up — better dry stiffness, slightly lower moisture uptake, higher HDT. It fills the gap when you need more thermal headroom than PA6 but can’t justify PPA pricing.
PPA+30GF is for parts that must perform outdoors under sustained load, year-round, across climate zones. The material premium pays for itself in field reliability. No retrofits. No creep surprises at year three. No modulus loss when the humidity spikes.
Running these numbers for your own outdoor part? Contact our engineering team for a material recommendation on your specific geometry and load profile.