Manufacturing · Stage 04b

EBM — Extrusion Blow Molding for HDPE, PE and PP Bottles

A tube of melt is extruded downward, the mold closes around it and air inflates it against the cooled wall. One continuous step from resin to a hollow body — which is why it carries most of the household, shampoo and body-care volume.

Quick answer

Extrusion blow is the route for opaque, high-volume bottles — and for every shape a preform cannot make

A parison — a tube of molten plastic — is extruded downward between the open halves of a mold. The mold closes, pinching the tube at both ends, and air inflates it outward against the cooled mold wall. The part is then trimmed free of the tail and flash.

There is no preform and no separate injection step for the body, which is why extrusion blow is economical at high volume and why it handles shapes injection stretch blow cannot: handles, off-centre necks, non-round profiles and deep grip panels. Wall thickness is controlled by programming the parison as it is extruded, so material can be put where the bottle needs it.

30+

Automatic blow lines

HDPE / PE / PP

Materials on this route

5–1,000 ml

Capacity range

SJE

PE mold numbering

22 · 427

HDPE · PE molds

200,000

Pieces per day

Scope of this page

This page covers the extrusion-blow route as a production process. For the PET stretch-blow route, see ISBM. For whether HDPE is the right material for your fill in the first place, see material comparison.

Six questions

Extrusion blow, answered in six questions

The same six questions apply to every manufacturing process on this site, so the answers can be compared stage by stage.

What is the process?

Resin is melted and extruded downward through a die head to form a hollow tube called a parison. The two halves of the mold close around the tube, pinching it closed at the top and the base. Air is blown inside and the tube expands outward against the cooled mold wall. After cooling, the mold opens, the part is removed and the tail and flash are trimmed. The trimmed material is regranulated and handled under the same controls as any other input.

Why does it matter?

Extrusion blow produces the bottle and its features in a single operation, so it is the most economical way to make an opaque high-volume bottle. It is also the only practical route to certain shapes: integrally molded handles, off-centre necks, non-round cross-sections and deep grip panels cannot be blown from a preform. The trade-off is that the wall is not biaxially oriented the way a stretch-blown PET wall is, and the pinch-off line at the base is a real stress point that has to be designed and tested rather than assumed.

What packaging does it produce?

HDPE, PE and PP bottles from 5 to 1,000 ml: shampoo and conditioner bottles, body wash and shower gel, hand soap, household and surface cleaners, bath and sanitiser bottles, and squeeze bottles with non-round profiles or handles. Opaque, coloured, pearlescent and soft-touch combinations all run on this route.

What quality issues should buyers watch?

Parison sag and unequal wall thickness, pinch-off and tail flash at the base, weld-line strength along the mold seam, drop-test performance on the filled and packed unit, weight control inside the ±2% band, capacity against the specified fill volume, colour consistency across the run, and ink adhesion if the bottle is printed.

What information does the buyer need to provide?

The capacity and fill volume, a shape reference or a drawing, the material or a reason to prefer one, a colour reference with a physical sample, the neck finish or the closure to be fitted, the fill product and its chemistry, the decoration plan, the shipping route, and the annual volume with how it is spread across the year.

What happens after this process?

Trimming and deflashing, then inspection, then decoration — polyolefin surfaces need a flame or water-hanging pre-treatment before printing, or the ink will peel — then closure matching, final QC, packing and export.

The cycle

The extrusion-blow cycle, step by step

Extrusion blow is often described as a one-step process, and it is, in the sense that the bottle is formed from melt without an intermediate part. It still has a sequence that has to be controlled stage by stage.

Melting and metering

PET and PE resin dried at 170–180 °C for 3–4 h; masterbatch at 100–120 °C for 2 h. The melt is metered at a stable rate, because parison weight is set here.

Parison extrusion

The die head extrudes a tube downward. Parison wall thickness can be programmed along its length, which is how extra material is placed at the shoulder and base without thickening the whole body.

Mold close and pinch-off

The mold halves close and pinch the parison shut at the neck and the base. The pinch-off geometry is designed into the tool — it is where base strength is won or lost.

Blow and cool

Air inflates the parison against the cooled mold wall. Cooling time decides both the dimensional stability of the part and the cycle time, and it is designed into the mold rather than set by feel.

Demold and trim

The part is removed and the tail and flash are trimmed. Regranulated trim is controlled and never used as a silent substitute for virgin resin.

In-process inspection

Weight against the ±2% band, wall thickness measured at four points, neck and thread dimensions, and visual defect inspection every 30 minutes while the run continues.

Handover

Bottles move to pre-treatment and decoration, or directly to closure matching when the specification has no decoration.

Defects

What a buyer should watch for, and how we control it

Extrusion-blow defects differ from stretch-blow defects in one important way: the controlling variables are the parison and the pinch-off, not the reheat profile.

Symptom	What it usually means	How we control it
Thin wall on one side; a bottle that dents under load	Parison sag between the die head and the mold, or a parison programme that does not match the shape. Material ends up at the bottom instead of around the body.	Parison programming set at first-article sign-off, then wall thickness measured at four points in process
Base failure or splitting on drop	A weak pinch-off weld at the base, or too little material in the base for the shipping route.	Base geometry agreed in the tool at design stage, plus a 1.2 m drop test on packed units at OQC
A visible witness line along the mold seam that opens under pressure	Insufficient weld-line strength where the two mold halves meet, often worsened by a cold mold or low blow pressure.	Drop and leak testing on the assembled unit at OQC, with mold temperature and blow pressure controlled at first-article stage
Weight outside the agreed band	Unstable extrusion rate, drifting melt temperature or regrind blended at an uncontrolled ratio.	Weight inspected in process against ±2%, with regrind handled under the same batch controls as virgin resin
Colour inconsistency across the run or between orders	Masterbatch dose drift, or a colour approved from a paper reference rather than a physical sample.	Colour matched against the approved physical master sample at IQC and again in process, under standard light
Print peeling or washing off in the filling line	Polyolefin surfaces are low-energy: ink will not bond to an untreated HDPE or PE surface, and the failure shows up after filling, not before.	Flame and water-hanging pre-treatment before printing, with print-adhesion testing before the run is released — see the decoration line
Capacity drifting from the specified fill volume	A parison or cooling change that moved the internal volume, which is invisible until the filling line over- or under-fills.	Capacity spot-checked against the approved specification in process and again on the finished lot

Most of these are set at the parison and the tool rather than at the machine, which is why extrusion blow starts with a specification and a sample rather than with a setting.

Inputs

What we need from you before extrusion blow can start

Extrusion blow can accommodate shapes that a preform cannot, so the shape information matters more here than in the PET route.

EBM project inputs

Capacity and fill volume

The nominal fill volume, plus the headspace or overfill allowance your filling line uses.

Shape

A drawing, a 3D file or a physical sample. If there is a handle, a grip panel or an off-centre neck, say so early — it changes the tool.

Material

HDPE, PE or PP, or the reason you prefer one. If the choice is open, the fill chemistry is what decides it.

Colour and effect

A Pantone reference plus a physical sample, and whether the finish is solid, pearlescent, frosted or soft-touch.

Neck finish and closure

The finish code, or a physical closure sample. The bottle is tested as an assembly rather than as a bare part.

Fill product

What goes in the pack. Alkaline cleaners, alcohol-based sanitisers and essential-oil blends each stress the material differently.

Decoration plan

Which process carries the artwork, how many colours, and whether the artwork is final. Printing on polyolefin needs pre-treatment, so this affects the schedule.

Shipping route

How the goods move and how far. The route decides how much drop and compression protection the pack needs.

Volumes

First order, annual volume and the run pattern across the year.

Destination market

Because it decides which documentation has to be prepared alongside production.

For the material decision behind this route, see HDPE, PE and PP, or compare all six materials side by side in the material comparison.

FAQ

Extrusion blow FAQ

Which materials run on the extrusion-blow route?+

HDPE, PE and PP. Our PE and HDPE mold libraries are numbered SJE. PET and PCR PET do not run on this route; they run on injection stretch blow.

Can you mold a bottle with a handle?+

Yes. An integrally molded handle is one of the reasons extrusion blow exists — a preform-based route cannot produce one. Send a drawing or a sample and we will confirm the tooling position.

Why do PE and HDPE bottles need pre-treatment before printing?+

Polyolefin surfaces are low-energy, so ink does not bond to them reliably. The bottles are flame- and water-hanging tested before printing to prevent ink peeling, and the print is adhesion-tested before the run is released. See the decoration line.

Can extrusion blow make a clear bottle?+

No. HDPE and PE are inherently translucent-to-opaque, and PP is hazy in thick sections. If clarity is the requirement, the material is PET and the route is stretch blow.

What wall thickness can you hold?+

Wall thickness is set by the parison programme and the shape, and it is agreed against a specification rather than quoted as a single factory number. In process it is measured at four points per cavity.

How does the base of an extrusion-blown bottle differ from a stretch-blown one?+

An extrusion-blown base has a pinch-off weld where the mold closed on the parison, so the base is a designed stress point that has to pass a drop test. A stretch-blown PET base is formed from solid preform material with no weld. Both are tested the same way — on the packed unit at OQC.

What is your MOQ on this route?+

From 5,000 pcs on a stock mold. Custom tooling starts higher, typically in the 10,000 to 20,000 piece range for the first order. See tooling and molds.

Where extrusion blow sits in the chain

EBM is stage 04b of eleven. Like ISBM it consumes prepared resin and hands a finished body to trimming, inspection, decoration and closure matching.

Manufacturing

Manufacturing hub →Injection molding →ISBM — stretch blow →EBM — extrusion blow →Tooling and molds →Decoration line →

Materials and engineering

Materials hub →Material comparison →Packaging engineering →Bottle design →Neck and closure →Formula compatibility →

Quality, process and reading

Quality & compliance →Quality & compliance — certifications →One-stop capability →How to choose between PET, HDPE and PP bottles →PET vs HDPE vs PP vs PETG: material guide →Virgin resin vs recycled resin: what to verify →

Send us the shape, the material and the fill.

We will confirm whether the geometry suits extrusion blow, and what the tooling and sampling position looks like.

Talk to Engineering Request a Quote

Part of Plastic Packaging Manufacturing: From Resin Pellet to Export | Shijin

Keep reading

Material, engineering and buying pages that this one sits next to.

Bottle Decoration: Printing, Labelling and Coating | Shijin Injection Molding: Preforms, Closures and Dispensers | Shijin ISBM: Injection Stretch Blow Molding for PET Bottles | Shijin Tooling: Stock Mold vs Custom Mold Explained | Shijin Quality & Compliance: ISO 9001, Testing and Documentation | Shijin Packaging Engineering: Bottles, Closures and Decoration | Shijin Custom Bottles, Jars & Dispensers — Wholesale

Products behind this page

Real items from the Shijin stock-mold library. Shown specifications are the published ones; a quotation is built from your own drawing and fill volume.

PET | 500 ml | SJT0472-500