Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
ISO 29469:2022 — Thermal Insulating Products — Determination of Compression Behaviour
Compressive strength and stress-at-strain testing for building insulation materials
Overview of Compression Testing for Thermal Insulation
ISO 29469:2022 specifies a method for determining the compression behaviour of thermal insulating products, applicable to all product types used in building construction. The standard provides procedures for measuring compressive strength (for materials that yield or rupture below 10 % strain) and compressive stress at 10 % strain (for materials that do not exhibit failure within this range). This distinction is critical because different insulation materials display fundamentally different stress-strain behaviours under compressive loads.
Rigid closed-cell foams (PUR/PIR, XPS) typically exhibit a distinct yield point, allowing calculation of true compressive strength. Soft fibrous materials (mineral wool) rarely yield, so their performance is characterised by compressive stress at 10 % strain instead.
The standard defines four key parameters: compressive strength (σₘ), compressive stress at 10 % strain (σ₁₀), corresponding strain at maximum force (εₘ), and compression modulus of elasticity (Ec). Together these provide a complete picture of a material’s load-bearing behaviour — essential for applications such as inverted roofs, floor insulation, or insulation beneath ground-bearing slabs.
Test Apparatus and Specimen Requirements
| Parameter | Specification |
|---|---|
| Specimen size options | 50, 100, 150, 200, or 300 mm square; original product thickness |
| Platen requirement | Rigid, polished, parallel platens ≥ specimen diagonal; ball joint if needed |
| Loading rate | Constant displacement rate = 0.1 × thickness per minute (± 25 %) |
| Preload | 250 ± 10 Pa; 50 Pa permitted for deformable products |
| Force measurement | Maximum permissible error ± 1 % |
| Displacement measurement | Maximum permissible error ± 5 % or ± 0.1 mm (whichever smaller) |
Specimens must be squarely cut with faces parallel to within 0.5 % of side length or 0.5 mm. The number of specimens shall be specified in the relevant product standard — at least five in the absence of such specification.
For cellular glass products, Annex A requires special capping of specimen faces to prevent localised edge crushing. The capping material must not significantly deform during the test, or its deformation must be accounted for in the displacement measurement.
Engineering Applications and Data Interpretation
Compression test results from ISO 29469 are used for design value derivation through application of safety factors. For inverted roof systems where insulation is placed above the waterproof membrane, the insulation must withstand permanent dead loads (gravel ballast, green roof build-up) plus maintenance traffic. The compressive stress at 10 % strain is typically used as the reference value with a safety factor of 2–3 depending on the application.
For underfloor and ground-bearing slab applications, short-term loads during construction (concrete pumping, material storage) may be higher than in-service loads — designers should consider both scenarios. The compression modulus of elasticity derived from the force-displacement curve is useful for finite element analysis of insulation in complex loading configurations.
The standard also provides guidance on anisotropic materials: where the principal compression direction is unknown, additional specimen sets cut in different orientations may be required — a crucial consideration for products with oriented fibre structures or moulded skins.
The 2022 edition (second edition) revised the cellular glass test protocol in Annex A, modified the conditioning temperature range, and clarified the preload procedure.
Frequently Asked Questions
Q: What is the difference between compressive strength and compressive stress at 10 % strain?
A: Compressive strength is the maximum stress at yield or rupture (when failure occurs below 10 % strain). Compressive stress at 10 % strain is reported when the material does not fail within 10 % deformation — most flexible and semi-rigid insulations fall in this category.
A: Compressive strength is the maximum stress at yield or rupture (when failure occurs below 10 % strain). Compressive stress at 10 % strain is reported when the material does not fail within 10 % deformation — most flexible and semi-rigid insulations fall in this category.
Q: How does specimen thickness affect results?
A: Specimens thinner than 20 mm may produce reduced accuracy. Results should not be extrapolated to other thicknesses — the standard explicitly warns against this. Each product thickness requires separate testing.
A: Specimens thinner than 20 mm may produce reduced accuracy. Results should not be extrapolated to other thicknesses — the standard explicitly warns against this. Each product thickness requires separate testing.
Q: Can the test be performed on products with facings?
A: Yes — integrally moulded skins that are retained in use should be tested intact. The facings or coatings may affect the compression behaviour and should remain as in the final product.
A: Yes — integrally moulded skins that are retained in use should be tested intact. The facings or coatings may affect the compression behaviour and should remain as in the final product.
Q: What is the significance of the compression modulus of elasticity?
A: The compression modulus (Ec) describes material stiffness below the proportional limit. It is used for structural design calculations involving insulation in load-bearing applications and for finite element modelling of insulation systems.
A: The compression modulus (Ec) describes material stiffness below the proportional limit. It is used for structural design calculations involving insulation in load-bearing applications and for finite element modelling of insulation systems.
