3D print living hinge: thickness, length and filaments that last

Yes, you can 3D print a living hinge, and the filament decides how long it lasts. Model the web 0.4 to 0.6 mm thick (two or three 0.2 mm layers), print it flat and solid, and use polypropylene (PP) or thermoplastic polyurethane (TPU) for a hinge that opens every day. Hinges in PLA (polylactic acid), PETG (glycol-modified polyethylene terephthalate) and nylon broke within 1,000 folds in testing, so they suit prototypes.

How thick should a 3D printed living hinge be?

A 3D printed living hinge should be 0.4 to 0.6 mm thick, with at least two layers, per the Protolabs Network (Hubs) design guide. At 0.2 mm layers that means two or three layers. QIDI gives 0.4 to 0.8 mm. Injection-molded polypropylene hinges are thinner, about 0.30 mm (0.012 in), too thin for most filament printers.

These are the numbers to model. Length means the web’s span across the fold, from one body to the other; width runs along the fold line.

Feature	Value to model	Source
Web thickness	0.4 to 0.6 mm (0.016 to 0.024 in), at least 2 layers	Protolabs Network (Hubs)
Web thickness, wider range	0.4 to 0.8 mm	QIDI, FacFox
Thickness floor	twice the print resolution: 0.5 mm for nylon at 0.254 mm	Fictiv
Web length, 180° fold	L = π × R (formula below)	Protolabs
Radius where the web meets the body	1.5 mm on the outside of the bend	3ERP
Hinge width	split a hinge longer than 6 in (152 mm) into two or more	Fictiv

For comparison, Protolabs starts a molded hinge at 0.012 in (0.30 mm) thick and about 0.060 in (1.5 mm) long, with a 0.030 in (0.76 mm) radius on the side that stretches. MatterHackers puts molded hinges at 0.25 to 0.38 mm against filament-printer layers of 0.20 to 0.25 mm, which is why printed webs run thicker.

How long should the web be?

Protolabs sizes the length from where the hinge sits, so that the web bends into a half circle when the part closes:

L = (fold angle ÷ 180) × π × R
180° fold:   L = π × R

R = distance from the faces that meet when closed
    down to the center of the web's thickness

A web level with the closing faces folds on a short span. One at the bottom of a deep box needs a long one. Protolabs adds that shorter hinges put more stress on the material than longer ones.

Why the printed web comes out thicker

Printed flat, the web’s thickness is a count of layers. Printed on edge, it is a count of extrusion lines, so it cannot be thinner than one line.

In an Embry-Riddle Aeronautical University study (Gribbins and Steinhauer, 2014), MakerBot Desktop would not slice a 0.3 mm acrylonitrile butadiene styrene (ABS) hinge in the vertical build orientation. 0.6 mm was the thinnest it would print, and those hinges measured 0.85 to 0.94 mm. Measure your web with calipers and adjust the model.

How to 3D print a living hinge

Pick the orientation first. Hubs and FacFox give the rule: build the hinge’s width up layer by layer, never its length. A web whose layers stack across the fold splits at the layer bonds. UltiMaker’s PP data sheet shows why: printed PP stretched over 800% before breaking in flat and on-edge samples, but 22.8% in upright samples, where the pull runs across the layers.

Two orientations follow that rule:

• Flat, with the web as the bottom layers. It needs no supports. In a published fold test that compared orientations, PLA hinges printed flat lasted 197 to 208 folds on average. Those standing on edge lasted 106 to 145. Raster angle, 0° or ±45°, made no significant difference.
• On edge, with the fold line vertical. Hubs and FacFox recommend this so each layer lays one continuous strand across the hinge. It can need supports, and the web’s thickness becomes a count of line widths.

Then set up the print:

• Print the web solid. The PLA hinges in that orientation test were printed at 100% infill with two perimeters (shells), at 0.25 mm layers.
• Break it in warm. The test hinges were flexed 10 times at 80 °C before testing. FacFox describes the same idea: warm the hinge until it flexes without melting, bend it back and forth, then hold it closed while it cools.
• Keep PP on the bed. Prusa lists PP’s main drawbacks as heavy warping and poor adhesion to PEI (polyetherimide) sheets. Use a PP sheet, PP tape on smooth PEI, or Magigoo PP on glass. Set the bed to 85 to 100 °C, add a 5 to 10 mm brim and print in an enclosure.

A hinge with a pin, or knuckles printed in place, is a different design that uses clearances instead of a flexing web.

Which filaments work for a 3D printed living hinge?

Polypropylene (PP) and TPU (thermoplastic polyurethane) are the filaments that work for a 3D printed living hinge meant to keep flexing. In a published fold test, printed PP hinges passed 1 million 180° folds, and TPU reached 2 million folds undamaged. PETG broke after about 860 folds, nylon 12 after about 200 and PLA after about 160.

The test is Balderrama-Armendariz et al., presented at the Solid Freeform Fabrication Symposium in 2016. Five hinges per filament, each with a 1.5 × 1.0 mm folding section in a 3.3 mm body, were printed flat and folded 180° about twice a second. The pull column is the axial load each hinge carried before it broke, in kilograms-force (kgf).

Filament	Folds to failure	Pull load at break	What else the sources say
PP (polypropylene)	980,520 to 1,130,002	29.9 kgf	UltiMaker lists living hinges among PP’s uses; warps and needs a PP bed surface (Prusa)
TPU (NinjaFlex)	over 2,000,000, no damage	27.3 kgf	moved under 0.59 kgf of pull; QIDI names TPU 95A for living hinges, and Hubs suggests a TPU hinge section on a dual-extrusion printer
PETG	733 to 960	66.9 kgf	the authors rate it for 800 folds and above
Nylon 12	126 to 276	66.6 kgf	Hubs and 3ERP name nylon (PA 11 or PA 12) for single-material hinges; the test used Stratasys Nylon 12 on a Fortus 400mc
PLA	136 to 211	80.6 kgf	MatterHackers: ABS and PLA lack the properties a hinge needs
ABS	not tested	not tested	a finite element analysis of a fused deposition modeling (FDM) ABS hinge found it yielding at a 10° bend (Gribbins and Steinhauer)

Those counts belong to that setup: a hinge of another shape, thickness or printer will fold more or fewer times. The design guides expect few folds from rigid filaments. Fictiv says printed hinges last tens to hundreds of flex cycles, and Hubs reports an FDM test hinge that failed after 25 folds. The Stratasys Direct design guide says FDM living hinges “can be used for a small number of cycles.”

Can you make a living hinge in PLA?

Yes, for a hinge that folds a few dozen to a few hundred times. PLA hinges in the fold test broke after 136 to 211 folds, though they carried the highest load of the five filaments, 80.6 kgf. The authors rate PLA and nylon for prototypes and “non-lasting folding products like packaging.” A lid opened every day needs PP or TPU.

How to design a living hinge box for 3D printing

Say you want a 60 × 40 mm parts box, 12 mm tall closed, printed flat in one piece in PP with a 0.4 mm nozzle at 0.2 mm layers. The two halves are trays, each 6 mm deep with 1.6 mm walls, laid side by side with their backs facing.

1. Web thickness: 0.6 mm, the first three layers. It joins the two floors along the back edge, the full 40 mm wide.
2. Web length: the web sits at the floor, so R is the tray depth minus half the web: R = 6 - 0.3 = 5.7 mm and L = π × 5.7 = 17.9 mm. Leave 17.9 mm between the back walls. Closed, the web curls into a half circle about 5.7 mm deep behind the box. For halves of different depths, average their two R values.
3. Lid lip: on one half, add an inner wall 1.2 mm thick that stands 3 mm above the rim and drops inside the other half. For a lid that holds, give it 0.20 mm per side, the snap or friction lid fit in the tolerance calculator. The other half measures 60 - 2 × 1.6 = 56.8 mm by 36.8 mm inside, so model the lip’s outside at 56.4 × 36.4 mm.
4. Test the fit: QIDI’s 0.20 to 0.25 mm per side assumes PLA or PETG. Print one half and the lip before the whole box.
5. Optional: Protolabs suggests splitting a wide hinge into several narrow ones, which takes less force to close and keeps the part working if one breaks. Its example turns one 0.8 in hinge into three 0.2 in hinges with 0.1 in gaps. For this box, three 10 mm webs with 5 mm gaps fit the 40 mm width.