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How to Select Rotomolding Raw Materials: A Practical Guide That Saves You From Costly Mistakes
Opening Hook:
A customer once told me, "I bought the cheapest LLDPE powder I could find.
Now my tanks are cracking after 6 months outdoors. What did I do wrong?"
The answer: raw material selection.
In rotomolding, your powder isn't just "plastic"—it determines
your part's impact strength, UV resistance, chemical resistance, and service life.
Choose wrong, and you're replacing parts (or losing customers) within a year.
Here's the practical material selection guide I give to every new StarWay customer.
While technically you can rotomold many plastics,
polyethylene (PE) accounts for ~85% of all rotomolded products.
Why? PE flows well as a powder, has low shrinkage, and is tough enough
for most applications—all at a reasonable cost.
Other materials (PP, Nylon, PVC) exist for specialty applications.
But if you're making water tanks, containers, or general industrial parts,
LLDPE is your starting point.
LLDPE = Linear Low-Density Polyethylene
Key properties:
- Good impact strength (even at low temperatures)
- Excellent stress crack resistance
- Easy to process (forgiving powder melt behavior)
- Cost-effective
But here's where most buyers get confused:
LLDPE isn't just "LLDPE"—it comes in grades optimized for different uses.
At StarWay, we always ask customers: "Where will this part be used, and what will it hold?"
That single question determines the grade. Most material problems come from buying
A "general purpose" powder for an application that needs a specialized grade.
- Drinking water → Food-grade LLDPE (NSF/61 certified)
- Chemicals → Chemical-resistant grade (check the compatibilitychart!)
- Nothing (structural part) → General purpose is fine
- Outdoors, full sun → UV-stabilized grade (essential in tropical climates)
- Outdoors, cold region → LLDPE with good low-temp impact (-40°C rating)
- Indoors → General purpose OK
- Fire safety needed? → Flame-retardant grade
- Need stiffer walls? → HDPE (but harder to process) or add ribs
- Need bright colors? → Make sure the pigmentsystem is compatible
Cheap powder = inconsistent melt flow = wall thickness variations.
One of our Indian customers switched to a premium grade and reduced reject rate from 12% to 2%. The powder cost more — but he saved money overall.
MFI tells you how "runny" the melted powder is.
Too high = part may sag. Too low = poor fusion at corners.
For most water tanks, MFI 3–7 g/10min is the sweet spot.
Powder from Supplier A and Supplier B may have different particle sizes distributions. Mix them, and you'll get unpredictable melting behavior.
StarWay recommends dedicating one mold to one powder supplier whenever possible.