Wire and cable is the first application the manufacturer lists for its two highest grades: SG1 for high-grade insulation materials, SG2 for electrical insulation together with film and general soft products. This guide is about what those two grades offer a cable compound and which specification figures decide the order.
The two insulation grades
| Grade | Viscosity band (ml/g) | Published uses |
|---|---|---|
| SG1 | 156-144 | High-grade electrical insulation materials |
| SG2 | 146-136 | Electrical insulation, film, general soft products |
SG1 sits at the top of the entire range. At 156-144 ml/g it is the highest molecular weight the plant produces, and the published application list reflects that: insulation work where the compound's mechanical performance carries the specification, not just its cost.
SG2 shares the insulation application but reaches into film and general soft products as well, which makes it the more common choice when a compounder buys one grade for a mixed product slate.
Why molecular weight matters in insulation
A cable insulation or sheathing compound is a soft, plasticised product, and its specification is a mechanical one as much as an electrical one: the extruded layer has to survive winding, pulling and installation without cracking.
Higher molecular weight is what buys that margin. It raises the strength of the cured compound, and it changes the plasticiser balance too — the same softness takes more plasticiser in a high-viscosity grade, and a compound holding more plasticiser stays flexible at lower temperatures. That is the general reason the insulation grades sit at the top of the viscosity range rather than the middle of it.
The indicators that matter for cable compounds
SG1 and SG2 are measured against the SG1-to-SG6 indicator set. The figures below are the published specification.
| Indicator | Premium | First grade | Qualified |
|---|---|---|---|
| Impurity particles (per 40 cm²) | 16 | 30 | 90 |
| Volatile matter incl. water | 0.3% | 0.4% | 0.5% |
| Apparent density | 0.45 g/ml | 0.42 g/ml | 0.40 g/ml |
| Fish eyes (per 400 cm²) | 20 | 40 | not specified |
| Residual vinyl chloride (mg/g) | 8 | 10 | not specified |
Two of these rows carry particular weight in insulation work.
Impurity particles are counted foreign matter in the resin. An insulation layer is thin by the time it is extruded, and a particle in the resin becomes a defect in that layer — a weak point exactly where the product can least afford one. The gap between 16 and 90 particles per 40 cm² across the three grade levels is the difference between a premium and a qualified resin, and it is the row to look at first.
Volatile matter is residual moisture. In a cable line it shows up as bubbles and surface defects in the extruded layer. At 0.3% against 0.5%, the premium level is the safer specification for a line running thin insulation at speed.
The residual vinyl chloride figure is the third row worth attention, and it has a guide of its own on this site because it is the figure regulators and downstream buyers check first.
Which grade level to order
For insulation compounds, the grade-level decision is about the standard the finished cable has to meet, not about appearance. Most cable work is opaque, so fish eyes are not a visible defect the way they are in clear film — but impurities and volatile matter still land in the extruded layer, and a rejected reel is expensive regardless of whether the defect was visible or electrical.
As a practical rule: compounders supplying to a customer specification usually run premium or first grade on insulation work, and the qualified level is the exception rather than the rule. If you are unsure which level your own specification needs, describe the finished cable and the standard it is sold against, and we will tell you what we would order.
What to send us
Tell us whether the material is for insulation or sheathing, the cable standard it has to meet, and the quantity in MT. We will confirm the grade, the grade level and the indicator figures we can hold for the batch — and quote against your destination port.