XPS insulation is a rigid board made from dense polystyrene foam. It is often considered under floors, in enclosed balconies, and along the bottom of exterior walls because it absorbs less water and withstands pressure better than soft insulation, but it does not replace waterproofing or a finished floor.
For coordinating insulation, floor height, and pressure
It suits enclosed balconies, floors, thresholds, and lower exterior walls where cold, moisture, heating pipes, and the finished floor height must be considered together.
- Enclosed balconies where insulation, underfloor heating, and threshold height need to fit together
- Floors where the insulation must resist the long-term weight of people and furniture
- The bottom of exterior walls where cold areas and board joints can be checked before finishing
Absorbing less water does not make XPS waterproof. Foam near flame, hot pipes, or fire-resistant walls and floors also needs suitable protection.
- The boards are expected to solve water entry and drainage without a separate waterproofing plan
- Hot pipes, flames, or fire-resistant walls and floors would be closed without protection
- The quote omits board thickness, resistance to pressure, joint filling, or the layers above it
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Calculate the finished floor height, not just the board
The insulation sits below heating, protection, and final flooring, so one board choice can change doors, thresholds, cabinets, and drainage levels.
- How high will the finished floor sit above the threshold?
- Add the XPS, heating pipes, the layer that spreads weight, adhesive, and final flooring. Check the total against doors, balcony thresholds, built-in cabinets, and drains before ordering.
- Will it withstand people and furniture over time?
- Choose a board made for the floor pressure expected in that room and check what spreads the weight above it. Thickness alone does not show how well the foam resists being compressed.
- How will the board joints and wall corners be filled?
- Decide what fills gaps between boards and where the floor meets the wall. Open joints leave a path for cold air, even when the rest of the floor is well insulated.
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Compare real products
These examples come from official manufacturer pages. Formats, facings and intended locations vary, so use them as a starting point rather than a ranking.
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| Market | Product | What it is | Official page |
|---|---|---|---|
| Korea | 벽산아이소핑크 | An XPS board range for interior and exterior walls, roofs, floors and refrigerated spaces, with grades and thicknesses for different locations. | Open |
| Korea | 부원화학부원핑크보드 | A rigid XPS board with a fine closed-cell structure, with published grades, heat-flow figures, weight-bearing information and available sizes. | Open |
| Japan | JSPミラフォーム® | An XPS insulation family for homes and buildings, with several grades ranging from general-purpose boards to higher-performance floor products. | Open |
| Japan | デュポン・スタイロスタイロフォーム™ | An XPS range with boards for general buildings, homes, foundations, roofs and cold-storage spaces, organized by intended application. | Open |
| United States | Owens CorningFOAMULAR® NGX® | An XPS board family for exterior walls, foundations, below-slab areas and roofs, offered in different strengths for different loads. | Open |
| United States | DuPontStyrofoam™ Brand XPS Insulation | An XPS product family with boards for residential sheathing, foundations, protected roofs and higher-load applications. | Open |
An XPS board range for interior and exterior walls, roofs, floors and refrigerated spaces, with grades and thicknesses for different locations.
A rigid XPS board with a fine closed-cell structure, with published grades, heat-flow figures, weight-bearing information and available sizes.
An XPS insulation family for homes and buildings, with several grades ranging from general-purpose boards to higher-performance floor products.
An XPS range with boards for general buildings, homes, foundations, roofs and cold-storage spaces, organized by intended application.
An XPS board family for exterior walls, foundations, below-slab areas and roofs, offered in different strengths for different loads.
An XPS product family with boards for residential sheathing, foundations, protected roofs and higher-load applications.
Official pages checked 2026-08-24 · Recheck pricing and availability at the linked page.
A question from INBOT
Review every floor layer from the XPS to the finish
When different trades quote separately, the total height and responsibility for filling board joints are easy to miss.
- Record the exact product, grade, thickness, resistance to pressure, and every area where it will be installed.
- Draw the threshold, heating pipes, drainage direction, layer above the XPS, and final floor height together.
- Include the cutting and filling method at board joints, wall corners, and pipes that pass through the floor.
- Design waterproofing separately, and confirm suitable protection where the foam is near flame or high heat.
You can also review floor insulation and balcony work or compare urethane insulation board.
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Use cold lines and hollow sounds to find a broken section
The boards are hidden after finishing, but a cold strip, hollow sound, or cracked surface can point to a gap or compressed area below.
- Keep the product name, board arrangement, joint details, and heating-pipe positions with photos taken before finishing.
- If one line stays cold or the floor sounds hollow and cracks, check the XPS and the layer above it instead of replacing only the surface.
- When leaks or condensation appear at the bottom of a wall, find the waterproofing or drainage cause before opening and replacing damaged boards.
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