Phone cases are the most common TPU application in FDM printing. Getting one right involves more than just loading a file and hitting print. This guide covers the settings, design decisions, and hardness choices that separate a case that works from one that fits badly and cracks on the first drop.
A PLA phone case looks fine and fits precisely, but it fails the one job a phone case exists to do. PLA is rigid. On impact, a rigid case transmits the force of the drop directly into the phone. The case may stay intact while the screen doesn’t. Or the case shatters, leaving the phone unprotected for the next drop.
TPU deforms on impact. The flexible material absorbs energy by changing shape momentarily, distributing the impact force across the case rather than concentrating it at the point of contact. This is the same principle behind any rubber bumper case. The material’s ability to deform and return to shape is exactly what makes it protective.
PETG is a middle ground that doesn’t work well as a case material. It’s tougher than PLA but still rigid enough to transmit impact rather than absorb it. For cases that actually protect, TPU is the correct answer.
95A is the standard for phone cases. The vast majority of phone case STL files are designed with 95A in mind. At 95A, the case is firm enough to keep its shape when handling the phone, flexible enough to snap on and off without permanent deformation, and soft enough to absorb impacts effectively. Start with 95A unless you have a specific reason to go softer.
87A produces a grippier, more flexible case. The same case geometry at 87A feels noticeably more rubber-like in the hand. It’s harder to put on and take off because the material deforms more readily, which means more friction against the phone’s frame. If grip in the hand is the priority, 87A is worth trying. The print is harder to execute and takes more patience to dial in.
98A for minimal flex. Some cases use 98A specifically for corner bumpers or combined rigid/flexible designs. At 98A the body of the case holds its shape almost rigidly but still absorbs corner impacts better than any rigid PLA case.
Full hardness comparison: TPU Shore Hardness Guide.
These settings are for 95A TPU on a direct drive printer. See the main TPU guide for the baseline settings and adjustment logic.
Nozzle: 225-235°C.
Bed: 45-55°C on PEI. TPU cases release cleanly from PEI once the bed cools. Don’t peel while warm.
Speed: 20-25mm/s. Phone cases have thin walls and overhangs at corners. Slow speed produces clean corner geometry and consistent wall thickness.
Wall count: 3-4 perimeters. This is the most important setting for case durability. A 2-perimeter wall will flex too much at the sides and may not hold its shape around the camera cutout. 3 perimeters is the minimum for a case that feels substantial. 4 perimeters adds stiffness without making the case difficult to flex on and off.
Top and bottom layers: 3-4. Same logic as walls. Fewer layers produce a flexible membrane; more produce a more rigid surface.
Infill: 15-25% gyroid or honeycomb. The infill in a phone case is the structure that connects the outer walls to the inner surface. Gyroid distributes flex evenly across the case. 15% is flexible enough to absorb impacts through compression of the infill structure; 25% adds rigidity. For a case that absorbs drops, 15-20% is the sweet spot.
Layer height: 0.16-0.20mm. Fine enough for good surface quality on the outer walls without excessive print time.
Retraction: 0.5-1.0mm direct drive. Keep it low to avoid holes in the thin case walls.
If you’re printing a downloaded STL, these points help you evaluate whether the file is well-designed. If you’re designing your own, they’re the things that distinguish a case that works from one that doesn’t.
Lip height matters more than anything else. The raised lip around the screen should be at least 1.0-1.5mm above the screen surface. When the phone falls face-down, the lip hits the ground before the screen does. A lip below 1mm provides no meaningful protection. Most commercial cases have a 1.5-2mm lip. Check this in your slicer before printing.
Corner geometry determines drop protection. Phone corners are the first point of contact in most drops. Case corners need enough wall thickness and material volume to absorb the impact. Thin, sharp corners with minimal material offer little protection. Cases with rounded, bulked-out corners perform significantly better in drops.
Button coverage needs to allow actuation. Button cutouts that are slightly too small will prevent the buttons from pressing. Cutouts that are too large leave gaps that collect dust and dirt. For downloaded files, check the cutout dimensions against your specific phone model’s button dimensions before printing.
Camera cutout clearance. Camera bumps vary significantly between phone models and generation within the same brand. A case designed for one model year may not clear the camera module of the next year’s model even if the overall dimensions match. Verify camera cutout clearance specifically, not just overall case dimensions.
Port cutout tolerances in TPU. TPU cases flex when you plug in a cable, which means the port cutout can deform slightly under force. A cutout that’s precisely sized may feel tight. Cutouts 0.5-1mm larger than the port opening are more practical with TPU than with rigid materials.
Printing at the wrong speed. TPU phone cases attempted at 40-50mm/s produce inconsistent walls, stringing through cutouts, and poor corner definition. The case looks rough and fits poorly. Drop speed to 20-25mm/s.
Too few walls. A 2-wall case feels flimsy and the outer surface prints with visible gaps. 3-4 walls is the minimum for a case that feels like a real product.
Not letting the bed fully cool before removing. TPU at 50°C is soft. Pulling a case off a warm bed distorts the flat back surface and produces a case that doesn’t sit flat against the phone. Wait until the bed is below 30°C.
Printing without a purge line. TPU needs 5-10cm of consistent flow before hitting the model. Without a purge line, the first section of the first wall is often under-extruded, producing a visible gap at the start point. Enable the purge line option in your slicer.
Using a Bowden printer. Bowden extruders and TPU cases produce inconsistent extrusion, blobs on long straight walls, and usually a failed print before the case is complete. Direct drive is required for reliable TPU case printing.
TPU cases off the printer have a slightly rough matte texture from the layer lines. For most use cases this is fine and actually provides grip. If you want a cleaner surface finish:
Light sanding with 400-600-grit smooths the outer surface without significantly affecting fit. Wet sanding produces better results. Don’t try to sand TPU to a glossy finish — the material is too soft for high-grit polishing and will just move rather than cut.
Stringing inside cutouts is the most common finish issue. Small strings bridging across port cutouts or button openings are easy to remove with tweezers or a hot needle. Don’t pull at them from one end — this can deform the cutout edge. Cut them with scissors first, then clean up the stubs.
TPU does not take paint without specialised flexible paint or primer. Standard acrylic paint will peel off a TPU case after a few flex cycles. If colour is important, print in the right filament colour from the start.
eSUN TPU 95A is consistent across spools and runs reliably at the settings documented here. For phone cases specifically, colour consistency matters — cases are handled every day and any variation in the filament shows on the outer surface. eSUN’s colour consistency is solid.
eSUN TPU is available through the eSUN Official Store.
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Looking for more print-ready models and material guides? Both are at orefly.com.