Blow Molding for Hollow Bottles, Containers and Tanks
A hot tube of plastic is blown out against a cooled mold, so the hollow part comes out in one piece with no seams to weld. Send your design and an engineer checks wall thickness, neck and parting line before quoting the mold and the parts.
Compare all molding methods- Hollow part, no welded seams
- 1 piece
- Common materials
- HDPE, PP, PET
- Mold ownership from day one
- Yours
- Quote after we get your file
- 24 hours
How Blow Molding Works
In extrusion blow molding, molten plastic is pushed down as a hollow tube called a parison. The two mold halves close around it, air inflates it against the cool mold walls, and the part sets in the shape of the cavity. Then the mold opens and the flash is trimmed off.
- 01
DFM review of your part
We check wall distribution, corner radii, the neck finish and where the parting line will run.
- 02
Mold build
The two-half blow mold is designed with its cooling and pinch-off edges, then machined.
- 03
Parison and blowing
Hot plastic is extruded as a tube, the mold closes on it and air blows it out to shape.
- 04
Trimming and checks
Flash at the neck and base is trimmed off, and wall thickness and neck size are checked.
- 05
First samples and production
You approve first samples on video, then in hand, before production and shipping.
Is Blow Molding Right for Your Part?
Blow molding is the low-cost way to make hollow plastic parts at volume. Here is what it holds, and when another process fits better.
Typical blow molding figures
- Tolerance
- About ±0.3 to ±0.8 mm, tighter at the neck
- Wall thickness
- About 0.5 to 3 mm, thinner at corners
- Materials
- HDPE, LDPE, PP, PET
- Typical parts
- Bottles, containers, reservoirs, ducts
- Best-fit quantity
- Several thousand parts a year and up
- First samples
- About 4 to 8 weeks after design sign-off
Typical values from public blow molding guidelines. There is no published CADLETE blow molding project yet, so your quote and first samples confirm the figures for your part.
Choose blow molding when you need
- Bottles, jars and containers in one piece
- Reservoirs and tanks for liquids
- Hollow ducts and handles
- Light parts with little material
- Thousands of identical hollow parts
- Squeezable or impact-resistant walls
Consider instead
- Plastic injection moldingFor caps, closures and open containers with detailed walls.Plastic molding
- Family & multi-cavity moldsFor caps and small parts at high volume, several per shot.Multi-cavity molds
- 3D printingFor bottle shape and grip prototypes before the mold.3D printing
- Packaging boxesFor the retail box your bottle ships in.Packaging
Which Plastic Should Your Bottle Be?
Pick by what the part holds and how it is used: chemicals, heat, clarity or squeeze. We confirm the grade before the mold is built.
HDPE
Tough and chemical-resistant
The most common blow molding plastic: stiff, impact resistant and safe for many liquids.
- Density
- ≈ 0.95 g/cm³
- Service temp.
- ≈ −50 to 80 °C
- Tensile strength
- ≈ 20 to 35 MPa
Ideal forBottles, jerry cans, chemical containers
Polypropylene (PP)
Heat resistant
Light and stiff, and it takes higher temperatures than polyethylene.
- Density
- ≈ 0.90 g/cm³
- Service temp.
- ≈ −20 to 100 °C
- Tensile strength
- ≈ 25 to 40 MPa
Ideal forHot-fill containers, household products
PET
Clear and strong
Glass-clear with good barrier properties, the usual plastic for drink bottles.
- Density
- ≈ 1.38 g/cm³
- Service temp.
- Up to ≈ 70 °C
- Tensile strength
- ≈ 50 to 75 MPa
Ideal forBeverage bottles, clear containers
Typical published values. Grades vary, and your quote names the exact one.
Blow Molding Design Rules
In blow molding the plastic stretches as it inflates, so the walls thin out wherever the part reaches furthest. These recommended values keep the walls even.
Corners and edges
- Recommended
- Radius at least equal to the wall thickness, larger is better
- Why it matters
- Sharp corners stretch thin and crack
Depth of recesses
- Recommended
- Keep depth under the width of the opening, about 1:1
- Why it matters
- Deep pockets blow out too thin
Wall thickness
- Recommended
- Design for about 0.5 to 3 mm, expect it to vary
- Why it matters
- The thinnest point decides strength and leaks
Draft
- Recommended
- 1° to 2°, more on textured surfaces
- Why it matters
- Helps the part release cleanly from the mold
Neck and thread
- Recommended
- Use a standard neck finish where you can
- Why it matters
- Standard caps and closures fit with no new tooling
Flat panels
- Recommended
- Add a slight crown, ribs or a pattern
- Why it matters
- Large flat walls dent and bulge
| Rule | Recommended | Why it matters |
|---|---|---|
| Corners and edges | Radius at least equal to the wall thickness, larger is better | Sharp corners stretch thin and crack |
| Depth of recesses | Keep depth under the width of the opening, about 1:1 | Deep pockets blow out too thin |
| Wall thickness | Design for about 0.5 to 3 mm, expect it to vary | The thinnest point decides strength and leaks |
| Draft | 1° to 2°, more on textured surfaces | Helps the part release cleanly from the mold |
| Neck and thread | Use a standard neck finish where you can | Standard caps and closures fit with no new tooling |
| Flat panels | Add a slight crown, ribs or a pattern | Large flat walls dent and bulge |
Recommended values. Your DFM review confirms them for your part and plastic.
Blow Molding Questions
What can blow molding make?
Hollow plastic parts in one piece: bottles, jars, containers, jerry cans, reservoirs, tanks, ducts and hollow handles.
What is the difference between extrusion, injection and stretch blow molding?
Extrusion blow molding blows a hanging tube of plastic and suits containers and parts with handles. Injection blow molding starts from a molded preform and suits small, precise bottles. Injection stretch blow molding is the usual route for clear PET drink bottles. Tell us about your part and we confirm the right route.
How many parts does blow molding need to pay off?
Usually several thousand a year, because the mold has to be paid for. For a few prototypes, 3D printing is the faster and cheaper way to check the shape.
Can I see blow-molded parts you have made?
We have no blow-molded client project in our published portfolio yet. Before production, you approve first samples from your own mold on video and in hand, so you judge the real parts.
Can you make the caps and the box too?
Yes. Caps and closures are usually injection molded, and we also make retail packaging boxes, so the bottle, cap and box can come from one team.
Who owns the blow mold?
You do, from day one, like every mold we build for you, with a mold passport and the written right to move it.
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Hollow part to make?
Get Your Blow Molding Quote
Send a 3D model or drawing with the volume, the neck and your yearly quantity. An engineer reviews it and replies with mold and part prices within 24 hours.
