EPS, XPS, polyiso and mineral wool boards: compare the actual product and location
A warehouse coordinator receives a request to use surplus roof polyiso under the loading-area slab. The same thickness is available, but the proposed product has not been compared with the specified slab board and loading requirements.
Start with the product name and intended location, rather than a ranking of four material families. EPS means expanded polystyrene; XPS means extruded polystyrene; polyiso means polyisocyanurate. Mineral wool boards are another product family. Current manufacturer information shows distinct facers, applications and restrictions within those names. A useful comparison therefore identifies the actual board and assembly, not a promise that every board of one family has the same strength, thermal performance or moisture behaviour.
Make the comparison answer the project question
- Identify the exact products and locations. List the specified and proposed products with thickness, grade, facing and current technical references. Link each to its actual roof, wall, foundation or slab detail. Record required approval status and Canadian applicability. A label such as “rigid foam” or a photograph of board colour does not identify the formulation, grade or permitted end use.
- Compare thermal information on the same basis. Read declared R-value or RSI, thickness and the relevant test or design conditions in the actual documents. Ask the responsible designer how the assembly calculation treats temperature, aging, facers and connections where relevant. Do not compare a centre-panel label with whole-assembly performance or multiply a remembered R-value per inch across every product. Mark missing information as a question rather than inventing an equivalent value.
- Check the requirements beyond thermal resistance. Compare loading and support criteria, moisture exposure, material compatibility, application temperature limits, protection and the required fire-related assembly evidence. Confirm which properties matter at the proposed location and who evaluates them. A roof-approved facer does not establish suitability below a loaded slab. Conversely, a product family name alone is not evidence that a specific board must fail.
- Submit the difference with a located decision. Give the reviewer a concise comparison, current product references, affected quantities and interfaces. Keep price or availability alongside the technical question, without treating them as approval. Retain the received outcome and any revised detail or inspection requirement before the order or installation changes. If different locations receive different answers, keep those boundaries clear for the receiving crews.
Common mistakes
- Identifying the product only by colour or family.
- Comparing thermal values with different bases.
- Ignoring loads, facers and required protection.
- Treating stock availability as technical acceptance.
Checklist
The board comparison retains
- Exact product, grade, facing and intended location.
- Thermal values with their declared basis.
- Relevant loading, moisture and assembly criteria.
- Missing evidence and responsible review.
- Received decision and affected orders or details.
Check your understanding
The offered board has the same thickness and a higher label R-value. Is it equivalent?
