SBS
SBS-modified bitumen
A thermoplastic elastomer: rubber-like stretch and recovery, also when cool.
- Top surface: mineral granules or film
- Upper SBS compound
- Carrier: polyester or glass fibre
- Lower SBS compound
- Burn-off underside film
▽ +09.00Comparison
SBS vs APP modified-bitumen membranes
Both are torch-applied modified-bitumen rolls. The difference is the polymer that modifies the bitumen — and that sets how the membrane behaves with heat and movement.
The two options
APP
APP-modified bitumen
A plastomer: a stiffer compound with a higher softening point that copes with heat and UV.
- Top surface: mineral granules or film
- Upper APP compound
- Carrier: polyester or glass fibre
- Lower APP compound
- Burn-off underside film
The roll is built the same way in both: only the polymer in the compound changes. Illustrative drawing, not to scale.
The key difference
Bitumen on its own turns brittle when cold and soft when hot, so it is modified with a polymer. SBS (styrene-butadiene-styrene) is a thermoplastic elastomer that gives the membrane stretch and recovery; APP (atactic polypropylene) is a plastomer that raises the compound’s softening point and makes it stiffer.
The carrier (polyester or glass fibre), the surface finish, the thickness and the number of layers are chosen separately from the polymer. Choosing SBS or APP is one decision among several that the specification and the product TDS settle.
Criterion by criterion
Descriptive criteria, not scores: each cell states the usual behaviour; final values follow the product TDS and the approved specification.
| Criterion | SBSSBS-modified bitumen | APPAPP-modified bitumen |
|---|---|---|
| What it is | Bitumen modified with an elastomer (rubber-like polymer). | Bitumen modified with a plastomer (plastic-like polymer). |
| Behaviour with heat | A lower softening point than APP; stays flexible as temperatures drop. | A higher softening point; keeps its body on hot roof surfaces. |
| UV exposure | Needs a protected surface (mineral granules or a coating) if left exposed. | Copes better with UV and heat; still needs a surface made for exposure, by product. |
| Movement capability | Stretches and recovers; better over substrates with thermal or structural movement. | Stiffer, with less elongation; better suited to stable concrete decks. |
| Installation method | Usually torch-applied; some products are made for cold adhesive or hot bitumen. | Almost always torch-applied. |
| Detailing | Folds easily at corners and upstands. | Needs careful heating at folds because it is stiffer. |
| Typical applications | Roofs, basements and foundations — especially where movement is expected. | Roofs exposed to sun and heat, and stable decks. |
| Protection requirement | Under tiles or backfill: a protection board or screed. Exposed: a cap sheet made for exposure. | The same: protection under tiles and backfill, and a suitable cap sheet if left exposed. |
| Substrate & moisture | Sound, dry, clean concrete, a bitumen primer and fillets at internal corners. | The same. |
| Repairability | Patched with a compatible sheet after cleaning and priming. | Patched with a compatible sheet after cleaning and priming; compatibility per the manufacturer. |
| Site safety | Hot work: a hot-work permit, a fire watch and extinguishers. | Hot work: the same controls. |
When to choose which
SBS
Choose SBS when
- Substrates where thermal or structural movement is expected.
- Two-layer systems where movement tolerance at the laps matters.
- Below-grade work where the specification calls for an elastomeric membrane.
APP
Choose APP when
- Roofs exposed to high solar heat, especially with a cap sheet made for exposure.
- Stable concrete decks with little movement.
- Where the specification or the consultant’s approval names APP.
Either way
- Laps, details and the protection layer affect performance more than the polymer does.
- The two are combined in one system only where the manufacturer’s system provides for it.
- On roofs crowded with penetrations, a liquid membrane may detail more easily.
General educational content; final values and requirements follow the manufacturer’s TDS and the approved project specification.
Common questions
Which one lasts longer?
Service life depends on the product, the build-up, exposure, protection and workmanship — not on the polymer alone. Warranty according to the approved system, manufacturer recommendations and the project agreement.
Do SBS and APP behave differently when left exposed?
In both, the cap sheet must be made for exposure (mineral-surfaced or suitably coated). APP usually tolerates heat and UV better, while SBS keeps more flexibility in cold and under movement.
Does the polymer change the surface preparation?
No. Preparation is the same: sound, dry concrete, a bitumen primer, fillets at corners and correct falls on roofs.
References
Standards that cover these materials — named to show what they cover, not to claim that any product complies.
- ASTM D6164Specification for SBS-modified bituminous sheets with polyester reinforcement.
- ASTM D6222Specification for APP-modified bituminous sheets with polyester reinforcement.
- EN 13707Reinforced bitumen sheets for roof waterproofing: definitions and characteristics.
- EN 13969Bitumen damp-proof sheets, including basement tanking sheets.
Technical review
Still weighing the options?
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