SBS Membrane Type I vs Type II: Grades & Selection Guide

Quick Answer: What Is the Difference Between Type I and Type II SBS Membrane?

Type I and Type II are the two performance grades of SBS membrane in the GB 18242 / GB/T 18242 standard series, and Type II is the higher grade. Under the former GB 18242-2008 requirements, Type II was specified with higher thresholds: 105°C heat resistance (Type I: 90°C), -25°C low-temperature flexibility (Type I: -20°C), and higher tensile and elongation requirements (at least 800 N/50mm and 40% for polyester reinforcement, versus 500 N/50mm and 30% for Type I). GB/T 18242-2025 is now the current standard; confirm current limits with the latest standard and the manufacturer’s TDS. Grade is independent of thickness: a 4mm Type I and a 4mm Type II are different products. Type II is commonly selected for cold climates, hot dark roofs, higher tensile requirements and projects where the specification or contract requires it.

What Are Type I and Type II Grades?

The grade is a material performance classification set by the standard, not a brand tier and not a thickness. In the product marking, the grade appears right after the membrane type — for example SBS II PY 4mm PE means: SBS membrane, Type II grade, polyester (PY) reinforcement, 4mm nominal thickness, PE film surface. Type I and Type II differ on three dimensions:

1. Heat resistance — the specified test temperature at which the membrane must show no flow, dripping or other failure under the standard test method (90°C for Type I, 105°C for Type II under the former GB 18242-2008 requirements).
2. Low-temperature flexibility — the specified test temperature at which the membrane must remain crack-free during the standard flexibility test (-20°C for Type I, -25°C for Type II).
3. Mechanical requirements — tensile strength and elongation, which are higher for Type II.

Type I vs Type II: Performance Compared

The values below are from the former GB 18242-2008 requirements. The current standard is GB/T 18242-2025 (effective 2026-05-01); confirm current limits with the latest standard and the manufacturer’s TDS.

Property	Type I	Type II
Heat resistance	90°C — no flow or drip	105°C — no flow or drip
Low-temperature flexibility	-20°C — no crack	-25°C — no crack
Peak tensile — polyester (PY)	≥500 N/50mm	≥800 N/50mm
Elongation at peak — polyester (PY)	≥30%	≥40%
Peak tensile — glass fiber (G)	≥350 N/50mm	≥500 N/50mm
Watertightness (30 min)	0.3MPa (G: 0.2MPa)	0.3MPa
Low-temperature flexibility after heat aging	-15°C	-20°C

Two numbers worth noticing:

• The 5°C test margin. Type II is tested at -25°C versus -20°C for Type I. The additional test margin gives Type II more low-temperature performance headroom than Type I, which can be valuable in colder service environments. It should not, however, be interpreted as a direct field failure temperature — actual system performance also depends on the substrate, reinforcement, installation quality and system design.
• Heat aging shifts the rating. Under the former standard, after 10 days of heat aging the low-temperature rating relaxes to -15°C (Type I) and -20°C (Type II). A membrane that barely passes its fresh-state rating may fail after aging — another reason the extra margin of Type II can matter on demanding projects.

Decision Summary

If your priority is…	Consider
Standard moderate-condition specification	Type I may be sufficient
Greater tested cold flexibility (e.g., cold regions)	Type II — tested at -25°C vs -20°C
Greater tested heat resistance (e.g., dark exposed roofs)	Type II — tested at 105°C vs 90°C
Higher tensile requirements	Type II — ≥800 N/50mm (PY) vs ≥500
Structural movement or settlement	Evaluate reinforcement type (PY) as well as grade
Contract explicitly requires Type II	Type II required

When Should You Specify Type II?

Type II is commonly selected where additional tested temperature or mechanical performance is required. It may also become mandatory when explicitly required by the project specification, tender document or contract.

Condition	Why Type II is often selected	Verify with
Winter temperatures approach or fall below -20°C	Lower tested flexibility temperature (-25°C)	Project design temperature + TDS
Roof surface temperature approaches 90°C (dark exposed roofs in hot regions)	Higher tested heat resistance (105°C)	Roof system design
Higher tensile requirements	Stronger specification (≥800 N/50mm PY)	Tender documents
Contract or specification explicitly requires Type II	Contractual requirement	Tender documents

Where substrate movement or settlement is expected, reinforcement type — particularly polyester (PY) — and the overall waterproofing system must be evaluated in addition to grade; see our PY vs G vs PYG Reinforcement guide. For moderate climates with stable conditions and no special contractual terms, Type I can be adequate and more economical. The grade is part of the product code, so confirm the required grade in the project specification before ordering — it cannot be upgraded after the membrane is manufactured.

Grade vs Thickness vs Reinforcement: Three Independent Variables

Grade, thickness and reinforcement are separate specification variables, and each controls different properties:

• Grade (Type I / II) controls tested temperature performance: heat resistance, low-temperature flexibility and the associated tensile/elongation minimums.
• Thickness (3mm / 4mm / 5mm) affects material content — soluble content rises from about 2,100 g/m² at 3mm to 2,900 at 4mm and 3,500 at 5mm — and with it puncture resistance and system robustness. Service life also depends on formulation, reinforcement, installation quality and exposure conditions.
• Reinforcement (PY / G / PYG) controls how the membrane responds to movement and load: polyester stretches, glass fiber stays dimensionally stable.

A common specification error is treating them as one decision. See our 3mm vs 4mm vs 5mm SBS Membrane guide for the thickness logic and PY vs G vs PYG Reinforcement guide for the carrier logic.

Three Common Misconceptions

1. “Type II is just a thicker Type I.” No — grade and thickness are independent. Type II is a higher performance grade with higher temperature ratings and tensile requirements; both grades are produced across the standard thickness range. A 4mm Type I and a 4mm Type II are different products.
2. “Type I means lower quality.” Type I is a compliant, standard-grade product for moderate conditions — not a reject grade. It is simply specified for projects where the higher Type II ratings are not required.
3. “The low-temperature rating means I can install it at that temperature.” No — the -20°C / -25°C rating describes the tested low-temperature flexibility of the finished membrane, not the installation temperature. Application conditions follow separate TDS rules: substrate preparation, priming and working conditions still apply. See our torch-application guide for installation details.

What to Specify When Buying

A complete SBS specification names the grade explicitly: SBS + grade + reinforcement + thickness + surface + standard — for example “SBS II PY 4mm PE, GB/T 18242”. A quotation that only says “4mm SBS” is incomplete, and the grade is the single most common omission.

When you compare suppliers, request the TDS and batch test report with every quotation and verify that the tested heat resistance, low-temperature flexibility and tensile values match the grade specified. Grade affects price — see our SBS price factors and B2B purchasing guide for the full comparison checklist. Our SBS Waterproofing Membrane product page lists Type I and Type II configurations with representative test values.

Frequently Asked Questions

What is the difference between Type I and Type II SBS membrane?

Type I and Type II are the two performance grades in the GB 18242 / GB/T 18242 standard series, and Type II is the higher grade. Under the former GB 18242-2008 requirements, Type II was specified with higher thresholds: 105°C heat resistance versus 90°C, -25°C low-temperature flexibility versus -20°C, and higher tensile and elongation requirements (at least 800 N/50mm and 40% for polyester reinforcement, versus 500 N/50mm and 30% for Type I). GB/T 18242-2025 is now the current standard; confirm current limits with the latest standard and the manufacturer’s TDS. Grade is independent of thickness — a 4mm Type I and a 4mm Type II are different products.

When should I specify Type II SBS membrane?

Type II is commonly selected where additional tested temperature or mechanical performance is required, and it becomes mandatory when explicitly required by the project specification, tender document or contract. As a general reference: cold-region projects where winter temperatures approach or fall below -20°C often choose Type II for its lower tested flexibility temperature (-25°C); dark exposed roofs where surface temperature can approach 90°C often choose it for the higher tested heat resistance (105°C); and projects with higher tensile requirements often choose it for the stronger specification. Verify the required grade against the project specification and the membrane TDS before ordering.

Is Type II SBS membrane thicker than Type I?

No — grade and thickness are separate specification variables. Type II is a performance grade with higher tested heat resistance, low-temperature flexibility and tensile requirements; thickness (3mm, 4mm or 5mm) affects material content, puncture resistance and system robustness. Available grade/thickness combinations depend on the reinforcement type, applicable standard and manufacturer. A 4mm Type I and a 4mm Type II are the same thickness but different products with different ratings and prices. Specify both values separately — for example SBS II PY 4mm PE.

Does Type II SBS membrane cost more?

Yes — Type II typically carries a price premium because the product must consistently meet higher performance requirements, which often requires tighter formulation, raw-material and production control. The premium is justified where the project demands it: cold climates, hot dark roofs, higher tensile requirements or contractual specification. To compare prices fairly, compare identical specifications — same grade, thickness, reinforcement and surface finish — and request the TDS and batch test report to verify the grade actually supplied.

Which SBS membrane grade should I choose for cold climates?

Type II is generally the preferred starting point for colder climates because its specified low-temperature flexibility test level is lower than Type I’s (-25°C versus -20°C under the former GB 18242-2008 requirements). The rating describes tested performance, not installation temperature — application conditions follow the TDS. Final selection should consider the project specification, design temperature, reinforcement type (polyester is generally preferred where settlement may occur) and the manufacturer’s TDS.

Technical References

• GB/T 18242-2025《弹性体/塑性体改性沥青防水卷材》 — current standard, effective 2026-05-01
• GB 18242-2008《弹性体改性沥青防水卷材》 — former standard, superseded
• Tianyuan Waterproof SBS TDS and batch test reports — available on request

Technical review: Tianyuan Waterproof Product Engineering Department.