How to Print Custom Phone Cases with TPU

Print phone cases in TPU 95A at 30–50 mm/s with 0.5–1.5 mm retraction on a direct-drive extruder, and design in 0.2–0.3 mm clearance per side for a snap fit. That combination gets you a case that installs without cracking, grips through elastic memory, and costs about $1–2 in filament. Everything below is the detail I wish I'd had before my first six failed attempts.

Which shore hardness should you use?

Start with 95A. TPU 95A is semi-rigid, prints nearly as easily as PETG, and flexes enough for a case without going floppy. Two walls with 10% gyroid infill makes it feel close to 85A without any of the printing headaches.

Shore hardness is a measure of a material's resistance to indentation, reported on lettered scales — the A scale for soft elastomers, the D scale for rigid plastics. The durometer scales are defined by indenter geometry and spring force, and each scale runs 0 to 100, with higher numbers meaning harder material. TPU (thermoplastic polyurethane) is a block copolymer with alternating hard and soft segments; the ratio between them sets the shore value, which is why TPU spans everything from gel-soft to nearly rigid.

My rule: if you have never printed TPU before, buy one spool of 95A and print three cases before touching 85A. I skipped that step, spent an evening watching 85A coil up inside the extruder, and learned nothing except patience.

Print settings that actually work

The three settings that decide whether a TPU print succeeds are speed, retraction distance and how dry the filament is. Everything else is fine-tuning.

Dry the filament. TPU picks up moisture fast, and wet TPU strings, pops audibly at the nozzle and bonds badly between layers. Four to eight hours at 50 °C in a filament dryer fixes it. Our filament types guide has drying temperatures for every common material.

Stringing is the biggest nuisance. Molten TPU is very fluid, so it oozes on travel moves. Keep retraction under 1.5 mm even on direct drive — long retractions just grind the filament — drop temperature in 5 °C steps if strings persist, turn combing on so travel stays inside the perimeter, and switch Z-hop off. That sequence has cleared stringing on every case I've printed.

One thing worth knowing about the hardware: all current QIDI machines use direct-drive extruders, which is why 85A is even on the table. A Q2 or any similar direct-drive printer feeds soft filament over a short unsupported path. In a long Bowden tube, 85A compresses like a spring instead of pushing forward.

Getting the fit right

Phone case fit lives in tenths of a millimetre, and TPU lets you run tighter clearances than any rigid material because the case stretches on installation and pulls back. Too tight and the corners crack going on. Too loose and it rattles and slides off in your pocket.

Print a test ring — just the bottom 5 mm of the case — before committing to a two-hour print. Too tight, add 0.1 mm horizontal expansion in the slicer; too loose, take 0.1 mm off. That fifteen-minute test has saved me at least six wasted full prints, which is exactly six more than I wasted before I started doing it.

Measure the actual phone with digital calipers. Published spec sheets are close but not exact, because curved edges and manufacturing variance both move the number. The same measure-model-test loop scales up to body-contact parts: our guide to custom finger splints from a scan covers the clearances a wearable needs, and ergonomic pruner handle aids applies the shore-hardness trade-off to grips that reduce hand strain rather than absorb a drop.

Design details that matter

Screen lip

Minimum 1 mm above the screen surface so the glass never touches a table face-down. Tempered glass protectors add 0.3–0.5 mm to the front profile, so I design a 1.2 mm lip as standard.

Camera bump

The camera module needs a 0.5–1 mm raised lip so the lens never contacts a flat surface. Chamfer the cutout edges — it prints cleaner.

Button overlays vs cutouts

Flexible overlays of 0.6–0.8 mm TPU over the buttons keep tactile feedback while shielding the switch. Open cutouts are simpler and harder to get wrong. I use overlays on the volume rocker and an open cutout on the power button, because I want to find that one by touch.

Charging port

Add 0.5–1 mm beyond the nominal USB-C opening. Cable housings vary in width more than you'd think.

Wall thickness

1.5–2.5 mm for the main walls, 3–4 mm at the corners where impact energy concentrates. Gyroid or honeycomb infill absorbs energy from multiple directions, which is what you want when the phone lands on an edge.

Where to find phone-specific models

Modelling a case from scratch in Fusion 360 takes two to three hours; finding an existing model takes two minutes.

• Universal Parametric Phone Case by PeteLaric on Thingiverse is an OpenSCAD design where you enter your phone's dimensions and it generates a fitted case. This is the best starting point for less common models.
• Thingiverse's phone case listings cover most mainstream handsets; search by the exact model name rather than the family.
• This TPU case design walkthrough covers wall thickness, lip height and drop-protection geometry if you want to model your own.

The common filaments collection lists the TPU options, and the wider filament range covers everything else.

Customisation is the whole point

You cannot buy a $10 commercial case with your name on it, a card slot on the back and a texture you chose. Printed, that's one job.

• Raised text or logo at 0.4–0.8 mm proud of the surface — visible in raking light without a second colour.
• Texture patterns (Voronoi, hex, diamond knurl) improve grip and hide layer lines simultaneously.
• A card slot sized for one or two cards: tight enough to hold through daily handling, loose enough for one-handed extraction.
• A kickstand, either as a snap-in piece or a living hinge built into the case body.
• A reinforced lanyard hole in one corner.

For TPU work beyond phone cases, our guides to TPU furniture feet, flexible cosplay armour and GoPro mounts with vibration damping push the same material in different directions. There are more ideas in our functional print roundup.

Frequently asked questions

Will a 3D printed TPU case protect my phone from drops?

From chest-height drops onto most surfaces, yes. TPU absorbs and spreads impact energy, particularly at the corners where a well-designed case runs 3–4 mm thick. It will not match a multi-layer injection-moulded rugged case with a separate rigid shell, and no printed case protects the screen face from a direct edge impact on concrete. For everyday knocks it works.

What shore hardness is best for a phone case?

95A for almost everyone. It flexes enough to install over the phone, stays firm enough to hold shape, and prints at normal speeds. Move to 85A when you want a softer, grippier feel and you already have TPU dialled in.

Can I print TPU on a Bowden extruder?

95A yes, if you drop to 15–25 mm/s and cut retraction right back. 85A on Bowden is frustrating — the soft filament compresses inside the long PTFE tube instead of advancing, and you get under-extrusion you cannot tune out.

How long does a printed TPU case last?

Twelve to twenty-four months of daily use in my experience. TPU does not yellow the way silicone does and holds its shape better across repeated install and removal cycles. When it does wear out, the replacement costs $1–2 in filament.

Why is my TPU case stringing so badly?

Wet filament first, retraction second. Dry the spool at 50 °C for 4–8 hours, then cap retraction at 1.5 mm, enable combing and disable Z-hop. If strings persist after that, drop nozzle temperature in 5 °C steps until they stop. Raising retraction distance is the instinctive fix and it is the wrong one — it grinds soft filament in the extruder gears.