Blow molding (typical)
- One-piece hollow parts without assembly
- Only the outside surface is defined by the mold
- Wall thickness varies with how far the parison stretches
Process comparison
Injection Molding vs Blow Molding: Hollow Containers vs Solid Features
Blow molding inflates a hot parison into a hollow shape. Injection molding fills a closed tool, which is how the caps, closures, and fittings are made.
Process choice
Hollow bodies versus precise molded features
The two processes often meet on the same product: the bottle and its cap.
Blow molding extrudes or injects a hot tube of plastic, closes a mold around it, and inflates it against the cavity. It makes hollow, closed shapes such as bottles, tanks, and ducts.
NetProto does not offer blow molding. Injection molding is the route for caps, closures, fittings, and any part that needs controlled threads or solid features.
Side by side
What each process shapes well
Hollow volume versus feature detail.
Injection molding (NetProto)
- Solid parts with inside and outside geometry defined
- Threads, snap rings, and tamper bands molded in
- Hollow shapes need two molded halves joined together
Routing table
Which process fits the part
Qualitative only.
| Part | Blow molding tends to fit | Injection molding tends to fit |
|---|---|---|
| Bottles and tanks | Closed hollow body | Not practical as one piece |
| Caps and closures | Not practical | Threads and seals held by the tool |
| Fittings and spouts | Rarely | Detailed geometry on every surface |
| Hollow housings | Simple outer shape | Two halves welded when inner features matter |
Quote inputs
Send this with the closure CAD
Closures and fittings are where molding usually enters a container program.
Container neck finish the closure must seal against
Resin for the closure and whether it must match the container
Tamper evidence or child-resistant requirements, if any
Annual volume across colors and sizes
Continue exploring
Related guides
Process first, then resin.
Compare hub
All comparison guides.
Compare hubInjection molding vs rotational molding
Large hollow parts versus detailed production parts.
Injection molding vs rotational moldingInjection molding vs extrusion
Constant profiles versus three-dimensional parts.
Injection molding vs extrusionUltrasonic welding vs adhesive
Joining molded halves into a hollow part.
Ultrasonic welding vs adhesiveFAQ
Common questions
Can injection molding make a hollow part?
Not as one piece in most cases. Two molded halves can be welded together when the part needs internal features a blow molded body cannot hold.
Does NetProto quote blow molded containers?
No. NetProto quotes the injection molded parts that go with them, such as closures and fittings.
Next step
Quote the closures and fittings in steel
Upload CAD for steel tool and piece price together. NetProto manufacturing is ISO 9001 certified.