Foam Filler vs PU Sealant
Foam fillers and PU sealants are widely used in construction for sealing and filling purposes. Although both materials help close gaps and joints, their properties, flexibility, and ideal applications differ significantly. Understanding these differences helps ensure correct material selection on site.
What Is Foam Filler?
Foam filler is an expanding polyurethane (PU) foam used to fill gaps, cavities, and voids. After application, it expands and cures into a semi-rigid structure that blocks air movement, improves insulation, and fills irregular spaces effectively.
What Is PU Sealant?
PU sealant is a polyurethane-based elastic sealant used to seal joints and cracks where flexibility and movement resistance are required. Once cured, it remains flexible and provides strong adhesion to construction substrates.
Key Differences Between Foam Filler and PU Sealant
1. Purpose & Application
- Foam Filler: Used for filling deep gaps, voids, and cavities where expansion and insulation are required.
- PU Sealant: Used for sealing joints, seams, and cracks where controlled flexibility is essential.
2. Expansion Behaviour
- Foam Filler: Expands significantly after application to fill empty spaces.
- PU Sealant: Does not expand; remains in the applied joint size.
3. Flexibility After Curing
- Foam Filler: Semi-rigid with limited flexibility.
- PU Sealant: Highly flexible and suitable for movement joints.
4. Insulation Properties
- Foam Filler: Provides thermal and acoustic insulation.
- PU Sealant: Primarily seals joints; minimal insulation effect.
5. Adhesion and Substrate Compatibility
- Foam Filler: Bonds well to porous surfaces like masonry, concrete, and wood.
- PU Sealant: Excellent adhesion to concrete, metal, aluminium, painted surfaces, and masonry.
6. Finish and Appearance
- Foam Filler: Requires trimming and surface finishing.
- PU Sealant: Provides a clean, finished joint appearance.
7. Water and Weather Resistance
- Foam Filler: Moisture resistant once cured but usually requires surface protection.
- PU Sealant: Excellent resistance to water, weather, and aging.
Best Use Cases
- Foam Filler: Door and window frame gaps, wall cavities, insulation voids.
- PU Sealant: Expansion joints, façade joints, floor joints, and external sealing.
Common Site Mistakes
- Using foam filler where joint movement is expected.
- Using PU sealant to fill deep cavities without backing material.
- Poor surface cleaning before application.
Companies Name
- Palco
- Bostik
- Soudal
- Sika
- Alcolin
Frequently Asked Questions (FAQ)
1. Can foam filler replace PU sealant?
No. Foam filler fills and insulates gaps, while PU sealant seals flexible joints.
2. Is PU sealant suitable for outdoor use?
Yes, PU sealants offer excellent weather and water resistance.
3. Can foam filler be painted?
Yes, after curing and trimming, it can be painted or plastered.
4. Does PU sealant allow movement?
Yes, it is designed to accommodate joint movement.
5. Should foam filler be protected?
Yes, exposed foam should be covered with plaster, paint, or sealant.
Raltro
Raltro is a construction knowledge platform focused on practical site guidance and correct material selection. By comparing foam filler and PU sealant, Raltro helps contractors and builders choose the right product for gap filling, joint sealing, and long-term construction performance.