Start With the Finished-Part Requirement
Before choosing PA6 or PA66, define the load, temperature, humidity, chemicals, electrical function, impact, dimensions, life, and required standards. Also record the part geometry, wall thickness, weld lines, flow direction, inserts, assembly loads, and molding process.
Rank the requirements instead of choosing the highest headline strength. A housing may depend on flatness and screw-boss retention. A bracket may depend on creep and fatigue; a connector on conditioned dimensions, electrical performance, and flame requirements. Compare exact grades at the actual service and conditioning state.
Specify Dry, Conditioned and In-Service States
Polyamides absorb moisture from their environment. Moisture can change dimensions and mechanical response, so a dry-as-molded value and a conditioned value are not interchangeable. The rate and equilibrium level also depend on grade, reinforcement, part thickness, temperature, relative humidity, and exposure time.
Define the state for every comparison. Use dry material for processing control, a specified state for inspection or assembly, and the expected service range. Record the conditioning method, time, temperature, humidity, storage, and measurement timing. Do not compare dry PA66 with conditioned PA6.
- Granulate moisture limit and drying instruction for the exact grade
- Part conditioning state used for dimensional and mechanical inspection
- Expected humidity and temperature range during storage and service
- Property and dimensional acceptance limits at each required state
Compare Temperature, Load and Toughness Together
PA66 often offers a higher melting and heat-performance direction than comparable PA6. The part decision still depends on reinforcement, stabilization, moisture, load, duration, and test method. HDT is a short-term comparative test. It is not a universal continuous-use temperature or a substitute for creep and heat-aging validation.
Stiffness, strength, elongation, impact and fatigue must be reviewed as a balance. Glass fiber can increase stiffness and load response while changing impact behavior, weld-line sensitivity and directional properties. Moisture may reduce stiffness while improving some toughness behavior. Use temperature- and condition-relevant grade data, then test the molded part under its actual load and failure mode.
Review Molding and Dimensional Risk
A change between PA6 and PA66 requires a fresh processing review. Use exact grade documents to confirm drying, handling, residence control, machine and mold guidance, hot runners, venting, gating, filling, cooling, ejection, and shutdown. Do not transfer one grade's settings without review.
For glass-fiber compounds, flow controls fiber orientation, directional stiffness, and shrinkage. Gate position, wall changes, ribs, bosses, weld lines, and cooling can affect warpage and dimensions. Establish the molding window and measure cavity-marked parts at a defined condition. Then compare dimensional performance.
Use Same-Filler Catalogue Examples Correctly
Taiyi Polymer EAG130 and EAG230 are both listed as 30% glass-fiber-reinforced compounds, which makes them useful for a controlled first comparison. In the current catalogue, EAG130 is the PA6 direction and EAG230 is the PA66 direction. Their data indicate different moisture and thermal directions while their room-temperature mechanical values remain grade-specific.
The table is not a family rule or an equivalence statement. Values are typical catalogue references obtained with the listed methods and specimen conditions. Confirm the current grade TDS, color, conditioning and processing guidance before using the numbers in a design calculation, specification, or replacement decision.
Taiyi GF30 catalogue example
Qualify the Exact Grade in the Intended Part
Mold traceable candidate parts in the intended tool and establish a stable process window for each grade. Record material condition, lot, fill time, transfer, pressure, cushion, part weight, mold-surface temperatures, cycle, cavity balance, appearance and scrap. Measure dimensions after agreed conditioning intervals rather than comparing parts at different moisture states.
Validate assembly, torque or retention, sustained load, fatigue, impact, heat aging, thermal cycling, humidity, chemicals, electrical function, flame or regulatory requirements as applicable. Release the exact grade and color only when molding capability, conditioned dimensions, functional evidence and required documents are complete.