We’re talking about two top-quality products from Sika, both based on STP technology (silyl-terminated polymers), but with features that can really make a difference depending on the application.
If you are choosing which one to use for your job, this guide will help you understand in a simple way which product is right for you.
What do they have in common?
Both Sikaflex 521 UV and Sikaflex 522 are one-component elastic adhesive sealants that cure with air humidity, making them practical to use, ready to apply, and suitable for both indoor and outdoor use.
Both offer:
- excellent adhesion to many materials
- weather resistance
- paintability
- solvent-free and isocyanate-free formulation
- professional bonding and sealing applications
So we are talking about two reliable, modern, and highly versatile products. But the differences begin when you look at performance in detail.
Sikaflex 521 UV: the versatile classic that always works
Sikaflex 521 UV has long been one of the most popular products for general applications. It is the classic "all-round" sealant that adapts to many everyday uses.
Its strength lies above all in ease of use and workability.
Why is it so popular?
Because it is:
- Easy to apply
- Highly workable
- Sanding after curing
- Resistant to sun, rain, and weathering
- Low odour
- Silicone- and PVC-free
If you are looking for a reliable, versatile product that is simple to use virtually anywhere, the 521 UV remains an excellent choice.
Sikaflex 522: the even more advanced new generation
Sikaflex 522 was created as a technological evolution for those seeking higher standards, especially in terms of air quality, biological resistance, and regulatory compliance.
It is not simply "another sealant". It is a product designed for more technical and professional environments.
What does it offer in addition to 521 UV?
Superior colour stability: the 522 preserves its colour better over time, even under strong UV exposure.
Mould resistance: a very important feature in damp or enclosed environments.
Ultra-low emissions and odour: ideal for indoor spaces, ventilation, and sensitive applications.
Professional certifications: this is where the 522 really makes the difference.
It has specific certifications for:
- Ventilation systems (VDI 6022)
- Indirect food contact (ISEGA)
- Low VOC emissions (EC1PLUS)
In practical terms: it is designed for those who want not only a high-performance sealant, but also one that complies with high professional standards.
So which one should you choose?
The answer depends on what you need to do.
Choose Sikaflex 521 UV if:
- you want a versatile product
- you are looking for ease of application
- you need a multi-purpose sealant
- you work in bodywork, marine, camper van, or general applications
Choose Sikaflex 522 if:
- you want a more advanced solution
- you work in technical or professional environments
- you need low emissions
- you are looking for greater long-term stability
- you operate in HVAC or food-related sectors
Our advice
If 521 UV is still one of the best multi-purpose sealants on the market today, the new Sikaflex 522 is the ideal choice for those who want to take quality to the next level.
More modern, more certified, more advanced. A true "next generation" of professional elastic sealants.
