Best Infill Patterns for Carbon Fiber Nylon: What a Print Tech Actually Runs

You switched to carbon fiber nylon for strength. Then the part still flexed under load, or the print took fourteen hours and a third of a spool. Nine times out of ten, the problem isn't the filament. It's the infill — the pattern, the percentage, and the walls around it.

I've run PA12-CF and PA6-CF on the bench for hundreds of hours. Here's what actually holds up in a functional part, and what's just wasting your time.

What Infill Really Does in CF Nylon

Carbon fiber nylon is stiff. The fibers carry tension along the layer lines, which is why a CF part feels so much more rigid than plain nylon. But infill is what keeps the part from crushing, buckling, or flexing through the middle.

Most people overthink the pattern and underthink the walls. On a load-bearing part, four or five perimeters do more for strength than any infill trick. Set walls to 4-5 before you touch the infill settings, then pick a pattern that doesn't fight you.

The Patterns We Run

Gyroid at 30-40% is the workhorse. It's isotropic — strength in every direction — and it prints clean at the higher speeds CF nylon likes. That's what we use for brackets, mounts, and anything that takes real load.

Cubic or triangular is fine when you need directional strength and know exactly where the load hits. Lightning is for cosmetic parts only — it saves time but contributes almost nothing to stiffness. Skip grid and line at low percentages; they leave long unsupported spans that turn into weak seams in nylon.

Percentage by Job

Load-bearing hardware: 40% gyroid, 4-5 walls. That's the bracket, the mount, the tool — the parts you'd trust with a wrench.

Stiffness without heavy load: 25% gyroid. Prototypes and fit checks: 15%. And if a part is mostly wall, you can drop the infill lower than you'd think — the walls are doing the work.

One warning: CF nylon is expensive. A 40% infill part drinks filament. If the part doesn't need it, don't print it.

What We Use

Our bench stock is IEMAI PA12-CF for structural parts — it's consistent, dries predictably, and the tested settings on our product page are exactly what we run in the shop. For non-critical parts where you don't need the full strength of nylon, Elegoo PETG-CF at 25% gyroid is a cheaper option that still prints stiff and dimensionally stable.

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