How to Choose a Blow Molding Resin
Start with the product requirements, not with a datasheet. Food contact, chemical exposure, stacking strength, clarity and cost all affect material choice.
Choose a material by answering four questions:
Key resin properties you will see on a datasheet
* Always use the exact values from the resin supplier, because each grade can be different.
HDPE — High-Density Polyethylene
The most common blow molding resin. Strong, chemical resistant, recyclable and economical.
Typical properties
Best suited for
Processing note
| Parameter | Indicative range |
|---|---|
| Melt temperature | 190–230 °C |
| Blow air pressure | 0.4–0.8 MPa |
| Screw speed | can be adjusted according to screw design |
Values are general guidance. Confirm with your grade supplier for optimum settings.
When a container holds aggressive detergent, solvent or chemical product, choose a high-molecular-weight HDPE grade and compare ESCR values from the resin datasheet. ESCR is often more important than impact strength for these products.
PP — Polypropylene
Good chemical resistance, heat resistance and a more rigid structure than HDPE. Can be translucent.
Typical properties
Best suited for
Processing note
| Parameter | Indicative range |
|---|---|
| Melt temperature | 220–250 °C |
| Mold temperature | 20–50 °C |
| Blow air pressure | 0.3–0.7 MPa |
PP can be sensitive to oxidation. Use stabilized extrusion-grade PP and avoid long dwell times at high temperature.
Choose PP when the container must withstand hot filling or when stiffness at high temperature matters. For simple cleaning bottles at low cost, HDPE is usually still the most economical choice.
PVC — Polyvinyl Chloride
Transparent and stiff. Used more often for technical or medical parts than for general packaging.
Typical properties
Best suited for
Processing note
| Parameter | Indicative range |
|---|---|
| Melt temperature | 170–190 °C |
| Danger threshold | above approx. 200 °C can start decomposition |
| Stabilizer | use a food / medical grade if required |
PVC processing requires a corrosion-resistant screw and barrel design.
PVC burns and releases hydrogen chloride if the melt temperature is too high. Thermal stability is managed by the stabilizer system. Ask your resin supplier for a grade that is already formulated for blow molding.
PETG — Glycol-Modified PET
Excellent clarity and impact resistance. Common for cosmetics, medical devices and display packaging.
Typical properties
Best suited for
Processing note
| Parameter | Indicative range |
|---|---|
| Drying temperature / time | 65–75 °C for 4–6 hours |
| Moisture limit | below approx. 0.02% |
| Melt temperature | 230–250 °C |
PETG must always be dried in a dehumidifying dryer before extrusion.
If PETG is not dried sufficiently, the polymer can hydrolyze during melting. This lowers molecular weight and makes the finished bottle brittle. A small dehumidifying dryer near the machine is strongly recommended.
Material Comparison Matrix
Use this as a short summary. Exact properties vary by resin grade and additive package.
| Property | HDPE | PP | PVC | PETG |
|---|---|---|---|---|
| Density (g/cm³) | 0.941–0.965 | 0.905 | 1.30–1.45 | 1.27 |
| General stiffness | Medium | High | High | Medium-high |
| Impact strength | Very good | Good | Medium | Very good |
| Chemical / ESCR | Excellent | Good | Good | Good |
| Clarity | Opaque | Translucent | Clear | Crystal clear |
| Hot-fill suitability | Limited | Good | Poor | Limited |
| Outdoor UV resistance | Good with carbon black | Poor without stabilizer | Good | Good |
| Typical temperature range | 180–230 °C | 200–260 °C | 170–190 °C | 220–250 °C |
| Food-contact options | Yes | Yes | Some grades | Yes |
| Relative cost | $ | $ | $$ | $$$ |
* “Food-contact options” means that food-contact compliant resin grades are available. Always confirm with the resin supplier and local regulations.
Practical Processing Tips
These notes are based on general extrusion blow molding experience. They help you avoid common production mistakes.
MFR and part size
Use a lower MFR resin for large, heavy containers so the parison does not sag. For small thin-wall bottles, a higher MFR grade may be easier to process.
Regrind percentage
Keep regrind under about 20–30% for good impact strength and consistency. If bottles need high ESCR or clarity, lower the regrind percentage further.
Always dry PETG
A small hopper dryer is not optional for PETG. Moist PETG gives cloudy or brittle containers. Drying at 65–75 °C for 4–6 hours is a typical starting point.
PVC temperature control
PVC works in a narrow temperature window. Check the melt temperature regularly and never leave PVC inside the barrel during a long stop.
ESCR means more than impact
For detergent or chemical drums, a normal HDPE with high impact can still crack when filled with a surfactant. Confirm ESCR with the resin supplier before sampling.
Blend test before production
Never trust a blend ratio from memory. Test the exact blend, color masterbatch and regrind on your actual machine before starting a long run.