How Much Infill Do You Actually Need?
Updated 2 min read
Infill is the setting customers ask us to raise most often, and it's usually the wrong lever. Understanding it will save you money on almost every order.
What infill actually is
Printed parts aren't solid. Inside the outer shell is a lattice, a honeycomb or wave pattern that supports the top surface and adds stiffness. Infill density is how tightly packed that lattice is. At 15%, roughly a sixth of the interior is plastic and the rest is air.
That air is doing more work than it looks like it is.
The three bands
10%: display and fit-check. Models, prototypes, decorative pieces, anything checking that a shape is right. This is the Light setting on a quote.
15-25%: general purpose. The default for most parts. Organizers, enclosures, mounts, brackets under light load. Standard is 15% and it is where we start unless something specific pushes us off it. Strong is 25%, for parts that get handled hard.
40%: load-bearing. Parts taking real force, absorbing impact, or holding a threaded insert. This is Very Strong on a quote, and it is the top of the useful range. Past it, returns fall off sharply.
Infill and walls, from above
Strength setting
A 40 mm part cut through and seen from above. The solid ring is the shell, and it is what carries most of the load. Try adding a wall, then try moving the density up a step, and watch which one costs more plastic for what it gives you.
Why more isn't better
Going from 15% to 40% roughly doubles material and machine time, so it roughly doubles what you pay, while adding maybe a third more strength. Two extra wall passes cost a fraction of that and often do more, because the shell carries most of the load.
So if you're paying for strength, pay for walls.
Solid is almost never the answer
100% infill is slower, heavier, more expensive and more likely to warp than a well-designed part at 40%. All that plastic shrinks as it cools, and a solid part has nowhere for the stress to go, which is what pulls corners up off the bed. We'll do it if you need the mass, but we'll ask why first.
When high infill is a symptom
If a part seems to need more than 40% to survive, the problem is usually somewhere else. Wrong material. A sharp internal corner starting a crack. Load running across the layers instead of along them. Cranking infill treats the symptom and bills you for it. Five minutes on the geometry is cheaper.
What to tell us
You don't need to pick a number. Tell us what the part does and how it's held. If we can hit the same strength for less by adjusting the walls instead, that's what you'll be quoted.