Nylon (PA) Injection Molding: A Buyer's Guide, Including Glass-Filled Grades

When a part needs to be strong, take wear, and survive heat and chemicals—gears, bearings, brackets, under-hood components—nylon is one of the first engineering resins buyers reach for. It’s a genuine workhorse of functional, load-bearing plastic parts, and it’s frequently reinforced with glass fiber to push strength and stiffness further. This guide covers nylon for buyers, as part of the material selection guide.

What Nylon Is

Nylon (polyamide, PA) is a family of engineering thermoplastics—the most common being PA6 and PA66—known for a strong balance of mechanical strength, toughness, wear resistance, and chemical and heat resistance. You’ll see it under names like Ultramid and Zytel. It’s often used glass-filled (e.g., 30% glass) to substantially increase strength and stiffness for demanding parts.

Why Buyers Choose Nylon

Characteristic	What it means for your part
High strength and toughness	Handles structural and load-bearing duty
Excellent wear / abrasion resistance	Suits gears, bearings, bushings, moving parts
Good heat resistance	Tolerates under-hood and elevated-temperature use
Good chemical resistance	Resists fuels, oils, and many solvents
Glass-filled grades available	Dial up stiffness and strength dramatically

Nylon’s combination of strength and wear resistance is why it dominates functional mechanical parts where a commodity resin wouldn’t survive.

The Two Things Buyers Must Plan For

Nylon is excellent, but it has two characteristic behaviors that shape every nylon program:

• Moisture absorption. Nylon is notably hygroscopic—it absorbs water from the air both during processing and in service. In processing, undried nylon causes splay and degradation; in service, absorbed moisture changes dimensions and properties. This is the single most important nylon fact for a buyer.
• Warpage, especially when glass-filled. Glass fiber boosts strength but shrinks differently along versus across fiber flow, making glass-filled nylon prone to warpage. On flat or precise parts this is a real design and tooling consideration.

Neither is a dealbreaker—nylon parts are made by the millions—but both must be planned for rather than discovered late.

Common Applications

Nylon is used for gears, bearings, bushings, and cams; automotive under-hood and structural components; power-tool and appliance parts; cable ties and fasteners; and a wide range of functional brackets and housings. Glass-filled grades go into the most demanding structural roles, sometimes replacing metal.

What Buyers Should Know About Molding Nylon

• Drying is essential. Nylon must be dried thoroughly before molding; molding it wet causes cosmetic and strength problems. A molder’s drying discipline is worth confirming.
• Design for warpage with filled grades. If you specify glass-filled nylon, treat warpage as a priority—uniform walls, gating, and tool cooling all matter, and tight flatness tolerances may be challenging.
• Account for moisture in tolerancing. Because nylon absorbs moisture in service and changes dimension slightly, discuss critical dimensions and the in-use environment with your supplier.
• Specify the grade. PA6 vs PA66, glass content, heat-stabilized or impact-modified grades—each changes properties, cost, and molding, so name the grade or the requirement.

Typical Processing Window

Nylon’s processing window is dominated by one requirement: it must be dry. PA is strongly hygroscopic, and molding it wet degrades properties and surface (it shows up as splay). The ranges below are illustrative for unfilled PA—glass-filled grades shrink far less, but more directionally:

Parameter	Typical range (unfilled PA)
Drying	~80 °C for 4 h or more — critical; PA absorbs moisture readily
Melt (barrel) temperature	~230–290 °C (PA6 lower, PA66 higher)
Mold temperature	~40–90 °C
Mold shrinkage	~0.8–1.5%+ (glass fill lowers it and makes it directional)

Illustrative ranges for unfilled grades, drawn from general industry processing references and a factory parameter table—not a substitute for the specific grade’s datasheet. Actual settings depend on grade, geometry, and machine, and filled grades differ (notably lower, more directional shrinkage). Confirm with the resin datasheet and your molder.

How Nylon Compares

Against acetal/POM—its closest rival for mechanical parts—nylon is generally tougher, more heat-resistant, and takes glass reinforcement well, but absorbs more moisture and is less dimensionally stable; acetal is more stable and lower-friction but harder to reinforce. Against commodity resins, nylon is far stronger and more wear-resistant at higher cost. Match the choice to load, wear, heat, and dimensional needs—see the material selection guide.

This is an independent buyer resource, not materials-engineering advice. Confirm the right nylon type, glass content, and grade with the datasheet and your supplier for your application.

Buyer FAQs

What is nylon used for in injection molding?

Nylon is used for strong, wear-resistant functional parts: gears, bearings, bushings, cams, automotive under-hood and structural components, power-tool and appliance parts, fasteners, and load-bearing brackets. Glass-filled nylon goes into the most demanding structural roles and sometimes replaces metal. It’s chosen when strength, wear resistance, heat, and chemical resistance are all needed.

Why does nylon absorb moisture, and does it matter?

Nylon is hygroscopic by nature—it absorbs water from the air both during processing and in use. It matters in two ways: undried nylon molds poorly (splay, degradation, weaker parts), so it must be dried thoroughly first; and absorbed moisture in service slightly changes the part’s dimensions and properties. Both need to be planned for, which is why drying discipline and tolerance discussions matter for nylon.

Why is glass-filled nylon so common?

Adding glass fiber—often around 30%—dramatically increases nylon’s strength, stiffness, and heat resistance, letting it handle structural loads and sometimes replace metal. The trade-off is that glass-filled nylon shrinks differently along versus across fiber flow, making it prone to warpage, and the glass is abrasive to tooling. It’s a powerful upgrade that needs design and tooling attention.

Nylon vs acetal (POM)—which is better for gears?

Both are used for gears, and the choice depends on priorities. Nylon is tougher and more heat-resistant and accepts glass reinforcement, but absorbs moisture and is less dimensionally stable. Acetal (POM) offers better dimensional stability, lower friction, and excellent fatigue resistance, with less moisture sensitivity. For high-load or hot applications nylon often wins; for precision, low-friction gears, acetal frequently does.