Most of the guides on this site answer a question about one grade. This one lays the whole range out on a single page, because the fastest way to the right grade is to see where the eight options split into three groups and which group your product falls into.
The published range at a glance
The table below follows the manufacturer's product parameter table for suspension PVC resin, translated from the published application list for each grade.
| Grade | Viscosity band (ml/g) | Specified for |
|---|---|---|
| SG1 | 156-144 | High-grade electrical insulation materials |
| SG2 | 146-136 | Electrical insulation, film and general soft products |
| SG3 | 136-127 | Electrical insulation, agricultural film, irrigation hose, general hose, artificial leather and footwear |
| SG4 | 126-119 | Industrial and agricultural film, tubing, artificial leather and high-strength pipe compounds |
| SG5 | 118-107 | Transparent products, rigid pipe and fittings, monofilament, sleeving, profiles and PVC-U windows |
| SG6 | 106-96 | Records, transparent sheet, rigid board and welding rod fibre |
| SG7 | 95-87 | Bottles, transparent sheet, rigid injection-moulded fittings and chlorinated PVC resins |
| SG8 | 86-83 | Bottles, transparent sheet, rigid injection-moulded fittings and chlorinated PVC resins |
The viscosity number is the measure of molecular weight the manufacturer publishes, and the average degree of polymerisation for industrially produced PVC resin in China is normally controlled within 590 to 1500. The band, not a single figure, is the specification — resin within a band behaves consistently in a process, which is what makes the grades interchangeable batch to batch.
Three bands, not eight grades
Read down the application column and the range divides into three groups.
The high-viscosity end, SG1 to SG4, is the soft-goods and cable territory. These are the grades for products that need melt strength and tear resistance: film, hose, artificial leather, footwear, wire insulation. The higher the viscosity, the more plasticiser a soft compound absorbs to reach the same softness, which is why the softest long-life products tend to sit at the top of the range.
The middle, SG5 and SG6, is rigid extrusion. Pipe, fittings, profiles, window frames, rigid and transparent sheet. The lower viscosity fuses faster than the top band, which is what a rigid extrusion line wants: the material has to complete fusion inside a fixed residence time without degrading.
The low end, SG7 and SG8, is bottles and injection moulding. The lowest molecular weight in the range gives the freest-flowing melt, which is what fills a thin-wall bottle preform or a multi-cavity fitting mould cleanly.
SG4: the grade in the middle
SG4 deserves a paragraph of its own because buyers overlook it. Its published applications — industrial and agricultural film, tubing, artificial leather and high-strength pipe compounds — straddle the soft and rigid groups, and that is exactly how to use it.
If a soft-goods compound needs more strength than SG3 gives you — a film that has to survive handling machinery, a hose with a pressure specification — SG4 is the next step up in molecular weight while staying in the same processing territory. On the rigid side, the published uses name high-strength pipe compounds: pipe formulations where toughness matters more than maximum output speed.
SG7 or SG8?
The two lowest grades carry an identical application list in the published table — bottles, transparent sheet, rigid injection-moulded fittings, chlorinated PVC resins — and both are measured against the same indicator set, which differs from the SG1-to-SG6 set in a few places we cover in the SG7 and SG8 guide.
In practice the choice between them is a processing decision. SG8, at 86-83 ml/g, is the lowest molecular weight in the range: the fastest-fusing, freest-flowing melt of the eight. SG7 trades a little of that flow for a little more strength in the finished part. Which one fits is a question about your mould and cycle time more than about your product, and it is worth settling with the technical manager before you fix the specification.
Narrowing it down
Three questions locate the grade:
- Soft or rigid? Soft points to SG1-SG4, rigid to SG5-SG8.
- What is the product? The application column above usually names it directly.
- What grade level? Premium, first grade or qualified — a decision about defect tolerance, covered in the grade-levels guide.
If your product is transparent, add a fourth question: the deciding figures there are the impurity count and the fish eyes, not viscosity.
Send us the product and the quantity and we will come back with the grade, the grade level and a quotation.