Views: 1347 Author: Sally Lyu Publish Time: 2026-07-31 Origin: Site
If SEBS is considered the all-rounder among styrenic thermoplastic elastomers, SIS is undoubtedly the tack specialist.
With its softness, low modulus and excellent compatibility with tackifying resins, SIS has become one of the most widely used base polymers in pressure-sensitive adhesives and hot-melt adhesive formulations.
SIS stands for Styrene-Isoprene-Styrene. It is an unhydrogenated thermoplastic block copolymer with an A-B-A “sandwich” structure:
End blocks: hard polystyrene segments
Midblock: soft polyisoprene rubber segment containing unsaturated double bonds
At room temperature, the polystyrene end blocks act as physical crosslinking points, providing strength and cohesion. The soft polyisoprene midblock gives the material its flexibility, elasticity and low modulus.
This combination allows SIS to behave like vulcanized rubber during use while remaining melt-processable like a thermoplastic during manufacturing.
SIS is often associated with high tack, but it is important to understand that SIS is normally not used alone.
In commercial adhesive formulations, SIS is usually combined with tackifying resins, process oils, plasticizers and antioxidants. Its strong compatibility with different tackifier chemistries makes it possible to balance initial tack, peel strength, cohesion and application viscosity.
High initial tack
Its low modulus allows an SIS-based adhesive to wet the substrate under light pressure, helping it develop adhesion quickly.
Good low-temperature performance
The soft polyisoprene midblock helps maintain flexibility and adhesive performance at relatively low temperatures. Actual low-temperature performance depends on the SIS grade and the complete formulation.
Low modulus and excellent flexibility
SIS-based formulations can conform easily to uneven surfaces and flexible substrates.
Good processing performance
Many SIS grades provide relatively low viscosity, good melt flow and excellent compatibility with tackifying resins, making them suitable for coating, spraying and other hot-melt processing methods.
Rapid setting after application
Hot-melt adhesives based on SIS can set quickly as they cool, supporting efficient production and high-speed converting lines.
Suitable for solvent-free hot-melt systems
SIS can be formulated into 100% solids hot-melt adhesives, avoiding the solvent drying and recovery processes associated with conventional solvent-based systems. SIS can also be used in solvent-based adhesives when required.
Because SIS contains an unsaturated polyisoprene midblock, it is generally more sensitive to heat, oxygen, ozone and ultraviolet exposure than hydrogenated elastomers such as SEBS.
Its main limitations include:
Lower long-term heat resistance than hydrogenated TPEs
Limited oxidation and outdoor weathering resistance
Performance that may decline under prolonged exposure to oils or aggressive solvents
Limited direct adhesion to some polar substrates without suitable tackifiers, primers or formulation adjustments
The actual performance limits depend on the SIS grade, tackifier system, antioxidant package, processing conditions and final adhesive design. Where long-term heat stability or outdoor aging resistance is critical, SEBS or another hydrogenated polymer may be more suitable.
SIS is one of the core elastomers used in hot-melt pressure-sensitive adhesives.
Typical applications include:
Packaging tapes and sealing tapes
Labels and self-adhesive materials
Protective films
Feminine hygiene products
Baby diapers and adult incontinence products
Construction, positioning and elastic attachment adhesives
Medical tapes and adhesive materials
Electrical and industrial adhesive tapes
Packaging and product assembly
Furniture and woodworking adhesives
Footwear bonding and repair adhesives
SIS is particularly important in hygiene products, tapes, labels, protective films, medical materials and packaging applications.
SIS can be an excellent choice when your adhesive requires:
Strong initial tack under light pressure
Good flexibility and surface wetting
Reliable adhesion at relatively low temperatures
Low processing viscosity
Fast setting after hot-melt application
A solvent-free hot-melt production process
A practical balance between adhesive performance and material cost
However, SIS may not be the first choice when the finished product must withstand prolonged high temperatures, strong UV exposure, severe outdoor weathering or aggressive oils and solvents.
With the right SIS grade, tackifying resin and formulation design, manufacturers can achieve an effective balance of tack, peel strength, cohesion, elasticity and processability.
For grade recommendations, technical data, reference formulations or sample evaluation, please contact our team.
