Clear TPU
- Soft and grippy, and absorbs drops
- Standard grades yellow with UV and age
- Strips off the core, so the tool is simpler
Molded part guide: phone cases
Injection Molded Phone Cases
A phone case wraps around the phone, which means its lip is an undercut on every edge. How that lip comes off the tool decides the tooling approach, and the resin decides whether it can simply be stretched off. Fit, drop protection, and a clear case that stays clear are the rest of the job.
Wrap-around
An undercut on every edge
Soft cases, hard shells, hybrid cases with bumpers, and rugged cases.
The lip that curls over the front edge of the phone holds the case on. In the tool, the case is molded around a core shaped like the phone, and that lip locks the part onto the core all the way round. Something has to let it go at ejection, and the answer depends almost entirely on the resin.
A soft TPU case can simply stretch. The ejector system pushes the case off the core, sometimes helped by air, and the lip flexes over the core and springs back. That keeps the tool simple. A hard polycarbonate shell cannot stretch that far, so its lip is formed by lifters or slides that move away from the part before it is pushed off. More actions mean a more complex tool.
Hybrid cases combine both: a hard PC back for stiffness and a soft TPU bumper around the edges for grip and drop protection. The bumper is overmolded onto the PC back, which needs a resin pair that bonds and mechanical locks where the TPU flows through the shell. Button covers are thin flexible sections with a small nub that presses the real button.
Fit is proven on real phones. Soft TPU shrinks by an amount that shifts with thickness and process, so the first cases are fitted to phones, not just measured. Clear TPU brings another issue: standard grades yellow with UV light and age. Aliphatic TPU grades resist this, and a light texture inside the case stops suction marks against the phone back.
Features
Case features and their jobs
Every feature is shaped by the phone it fits.
| Feature | Purpose | Design note |
|---|---|---|
| Wrap lip | Holds the phone in | Stripped off the core in TPU, lifters in PC |
| Button covers | Press through the case | Thin flexible section with a nub |
| Camera and port openings | Clear access | Raised lip around the camera protects the lens |
| Corner bumpers | Absorb drops | Thicker TPU or air pockets at the corners |
| Inner texture | Stops suction marks | Light texture or dots inside |
Tooling
Soft cases strip, hard cases need actions
The lip that wraps the phone decides how the tool releases the part.
- A flexible TPU case stretches over the core and is pushed off on ejection
- A hard PC shell cannot stretch, so its lip is formed by lifters or slides
- A PC back with an overmolded TPU bumper combines both
- Fit is proven on real phones since soft resin shrinks by varying amounts
Clear cases
Clear TPU or clear PC
Both are sold as clear cases. They age and protect differently.
Clear PC
- Hard, and stays clear and glossy longer
- Needs lifters or slides for the lip
- Scratches show on a glossy back
Drawing
What to send with a phone case
The phone model sets the core, the style sets the tool.
Phone model and its CAD or measured dimensions
Case style, soft, hard, or hard with a bumper
Button, port, and camera openings
Colors, clear or opaque, and inner texture
Printing or marking on the back
Expected annual volume
Keep reading
Related guides
Soft resins, overmolding, and the tooling actions hard shells need.
Wearable enclosures
Sealed shells worn on the body.
Wearable enclosuresOvermolding
Soft bumpers on hard backs.
OvermoldingTPU vs TPE
Choosing the soft resin.
TPU vs TPETPU
The usual soft case resin.
TPUPolycarbonate
Hard, clear shells.
PolycarbonateSide actions
Slides that form undercuts.
Side actionsSecondary operations
Pad printing and laser marking.
Secondary operationsConsumer products
How we support consumer programs.
Consumer productsMolded parts hub
Every part-type guide, grouped by family.
Molded parts hubFAQ
Questions about molded phone cases
Why do clear cases turn yellow?
Standard aromatic TPU grades yellow with UV light and age. Aliphatic TPU grades resist this, and clear PC stays clear longer as a hard case. Adding UV stabilizers helps, but the base grade matters more for a case that must stay clear for months.
Why is the case loose on some phones?
Soft TPU shrinks by an amount that shifts with thickness and process. The core is tuned after fitting early cases on real phones, and the process is then held steady. Keeping wall thickness even around the lip also makes the fit more predictable from shot to shot.
Can a hard case have a full wrap lip?
Yes, with lifters or slides that form the lip and move clear before ejection. The tool is more complex than a soft case tool. The lifters also leave witness marks on the inside of the lip, where they are out of sight.
How are logos and artwork applied?
Pad printing and laser marking are common secondary operations. Logos can also be molded in as raised or recessed lettering or as a texture change. Artwork on a clear case can also be printed on the inside face, so it does not wear off.
Next step
Quote a case for your phone model
Upload the case, or tell us the phone model and style. DFM feedback covers lip release, button covers, bumper overmolding, and fit.