PA6 and PA66 share the same polyamide family, but the two grades diverge sharply on heat and moisture behaviour that decide which one belongs in a given mold or die. PA6 is the lower-melt, higher-impact workhorse; PA66 is the higher-heat, stiffer, more wear-resistant option that is typically chosen for slides, wear strips, and ejector components inside the tool.
In practice, mold and die makers working in 2026 reach for unmodified PA6 for general non-critical wear parts, PA66-GF30 or PA66-GF50 for structural slides and bushings, and cast-nylon (MC nylon) for large wear plates where casting is more economical than injection molding [S2]. For tooling blocks and pattern equipment, the same moisture-control rules used for molded nylon parts carry over directly from the casting mold and mold base families.
PA6 vs PA66: Property Differentials That Drive Selection
The single biggest selection driver is heat deflection temperature: PA66 is consistently specified for tooling components sitting close to the mold cavity or die working face, where PA6 would soften under sustained load [S2]. PA6 absorbs more moisture than PA66, which means PA6 swells dimensionally and loses stiffness in humid shop environments, while PA66 retains a tighter dimensional envelope once conditioned. Tensile strength of unfilled grades clusters in the 70-85 MPa band for PA6 and climbs toward 80-95 MPa for PA66 once moisture is driven off, which is why PA66 wins for ejector pins and leader-pin bushings where stiffness matters.
Impact resistance tells the opposite story: PA6 absorbs more energy before fracture, so impact-loaded die components (drop-hammer inserts, knockout blade seats) often revert to PA6 even when the rest of the tool is PA66. Both grades process in the same family of injection-molding and extrusion equipment used to produce die casting pattern plates, with melt temperatures generally 30-50 °C apart between the two grades [S2].
Filled and Cast Grades: Glass, Carbon, and MoS2
Unfilled PA6 and PA66 rarely carry the load in a working mold or die. 30% glass-filled PA66 (PA66-GF30) is the most common structural grade for slides, gibs, and wear strips, raising heat deflection under load roughly 70-100 °C above the unfilled resin and pushing tensile strength past 170 MPa in conditioned state. 50% glass-filled variants push stiffness and creep resistance further and are used for thick-walled wear plates where deflection would shut down a die.
Carbon-fiber-filled grades (typically 10-30% carbon) cut friction coefficient below 0.2 against hardened steel, which is why carbon-filled PA66 is now standard for high-cycle ejector sleeves in progressive dies. For sliding interfaces where lubricant contamination is forbidden, MoS2-filled PA6 is still specified. Cast (monomer-cast, MC) nylon remains the economical choice for large wear plates, with castings routinely produced in thicknesses above 100 mm that injection molding cannot deliver cost-effectively.
Moisture Control and Drying: The Field Reality
Both PA6 and PA66 are hygroscopic and must be dried before any secondary machining, welding, or re-molding step [S2]. Practical shop data in 2026 keeps a dryer set-point of 80-90 °C for 4-6 hours for PA6 and 90-110 °C for 6-8 hours for PA66, with a -40 °C dew point air loop. Wet granules fed into a re-molding operation produce steam voids, drooling, and cracked moldings, all of which scrap the part.
For die components in service, the same moisture sensitivity means the as-molded dimension shifts after 24-72 hours of shop exposure, which is why precision wear parts are typically machined oversized and then conditioned before a final sizing pass. When nylon wear plates are used to back steel components in a sand casting mold pattern, the pattern maker compensates the original CAD model for the 0.5-1.5% swell typical of conditioned PA6.
Selection by Tooling Function: A Criteria Comparison
Specifying nylon for a mold or die in 2026 follows a function-led matrix. Wear plates and pattern backers: PA6 unfilled or MC nylon for low-cost, large-area coverage. Slide gibs and wear strips: PA66-GF30 for stiffness and creep resistance. Ejector and knockout components: PA66-GF30 for high-cycle tools, carbon-filled PA66 for unlubricated slides above 1 million strokes. Pattern plates for sand casting: dried PA6 sheet stock, with shrinkage allowance baked into CAD. Tooling fixtures and jigs for lighting equipment and electric lamps sub-assemblies: PA66-GF30, where dimensional stability under workshop heat matters more than absolute impact resistance.
PA6 typically costs less per kilogram than unfilled PA66, as PA66 commands a higher price because one of its main raw-material components is not domestically produced and PA66 offers greater heat and wear resistance. For nylon grades serving medical adjacent tooling (cleanroom fixture brackets, ESD-safe ejector trays), the same filled PA66 base is used but the recipe adds a conductive carbon or stainless-steel fiber load for static control.
What PA6 and PA66 Are Not For in Tooling
Neither PA6 nor PA66 belongs where the tool face runs above 200 °C continuously, where strong acids or bases attack the amide bond, or where the part sees sustained UV exposure without stabilization. Unfilled grades fail in load-bearing die components because their continuous-use temperature ceiling is far below the working face of a die casting die or an injection mold cavity. Above that ceiling, the choice moves to PEEK, PPS, or metal inserts, not higher-durometer nylon.
Field failures in 2026 mostly trace to two root causes: under-dried granules fed into a re-molding press, producing steam-blown parts, and glass-filled grades selected without a wear-direction orientation check, producing anisotropic wear that scrapes the mating steel surface. Specifiers who need a side-by-side look at how these tradeoffs line up against bearing and housing choices can compare against the Nylon (PA) Grades for Medical Devices: Selection Map and Spec Gates framework, since the underlying property rules and drying discipline are identical.
Standards, Spec Sheets, and Sourcing Signals
For sand-casting pattern plate work, also confirm the as-molded shrinkage (1.0-1.5% for PA6, 0.8-1.3% for PA66-GF30) so the CAD compensation matches the actual resin lot.
The next signal to track in 2026 is the roll-out of higher-recycled-content PA66 grades by European compounders, aimed at die and mold buyers with documented recycled-content targets, and the gradual displacement of MoS2-filled PA6 by carbon-filled PA66 in progressive-die ejector sleeves as cycle counts climb past 5 million strokes without lubrication.