Compressive Creep in XPS: What It Is and Why Floors Need It

8 September 2026

Compressive creep is the slow, time-dependent deformation of an insulation board under a sustained load that remains below its short-term compressive strength. For floors, this matters because even modest long-term settlement of the insulation layer translates directly into screed cracking, tile debonding, or loss of floor level — all without any single overload event. EN 13164 quantifies this property with the CC(2/1.5/50) designation, which sets the maximum creep deformation limit in kPa that the board can sustain for 50 years.

What Is Compressive Creep?

Compressive creep is the gradual, time-dependent reduction in thickness that a material undergoes when a constant compressive load is applied over a long period — even when that load is well below the board's short-term compressive strength. Unlike an immediate elastic deformation that recovers when the load is removed, creep is largely permanent.

For a thermal insulation board beneath a floor slab or screed, this means the board may continue to compress — slowly — throughout the service life of the building. Even a few millimetres of settlement can cause the screed to crack, floor finishes to debond, or drainage levels to shift in wet rooms.

How EN 13164 Measures and Declares Creep

EN 13164:2012+A1:2015 — the harmonised European product standard for factory-made XPS thermal insulation boards — defines a standardised creep designation: CC(2/1.5/50)X.

CC — compressive creep test method
2 — maximum allowable creep deformation: 2 % of original thickness
1.5 — stress applied during the test, expressed as a fraction of the declared compressive strength
50 — test duration extrapolated to 50 years of service
X — the maximum sustained compressive stress (in kPa) at which the board will not exceed 2 % deformation over 50 years

A higher X value means the board can sustain a greater long-term load without creeping beyond the 2 % limit. This number is therefore the key figure for floor designers selecting insulation under permanent loads.

Compressive Creep Values Across the PNP XPS Range

The following table summarises the declared CC values for PNP XPS grades that carry a compressive creep rating. Grades not listed in the table (XPS 150, XPS 150 W X-Grip, XPS 200, XPS 200 W, XPS 150 MG, XPS 200 MG) do not have a CC value in the available data — consult the current TDS for those products.

Product	Compressive strength class	Creep designation	Max. sustained load (kPa)
XPS 300 (boards > 30 mm)	CS(10\Y)300	CC(2/1.5/50)130	130 kPa
XPS 300 W (boards > 30 mm)	CS(10\Y)300	CC(2/1.5/50)130	130 kPa
XPS 300 MG	CS(10\Y)300	CC(2/1.5/50)90	90 kPa
XPS 500	CS(10\Y)500	CC(2/1.5/50)150	150 kPa
XPS 700	CS(10\Y)700	CC(2/1.5/50)210	210 kPa

Note that a high short-term compressive strength does not automatically mean a high creep limit. The CC value must be verified independently in the DoP and TDS for each product.

Why the Distinction Between Short-Term and Long-Term Load Matters

The short-term compressive strength class — for example, CS(10\Y)300, meaning ≥ 300 kPa at 10 % deformation or yield — characterises resistance to a load applied once, over a short duration. It is the correct property to check for impact resistance, installation loads, and transient events.

For a permanently loaded floor, the design load acts continuously for decades. The CC designation answers a different question: what is the highest sustained stress at which the board will deform by no more than 2 % of its thickness over 50 years? For XPS 300 and XPS 300 W (boards above 30 mm), the test showed that value is 130 kPa. For XPS 700 the test showed 210 kPa.

This supports the conclusion that selecting a product based solely on its short-term compressive strength class, without checking the CC value, can lead to underestimation of long-term settlement. A qualified structural or floor designer should verify that the applied permanent stress does not exceed the declared CC limit.

Practical Implications for Floor Design

Common sources of sustained load on underfloor insulation include:

Dead load of the screed and floor finish
Permanent live loads (racking systems, heavy machinery, cold-store shelving)
Self-weight of the slab above in floating-floor assemblies

If the sum of these loads, expressed per unit area (kPa), exceeds the declared CC limit, the insulation board may settle beyond 2 % thickness over the building's life. Even 2 mm of settlement in a 100 mm board can be significant in precision floors, wet rooms with drainage falls, or tiled finishes with rigid grout lines.

This alone does not prove that a specific product is suitable or unsuitable for a given project — that determination requires full load calculation by a qualified designer, reference to the current TDS and DoP, and compliance with the national application standard of the country of use. Contact PNP XPS technical support or consult the relevant documentation at the documentation page.

Sources

EN 13164:2012+A1:2015 — Factory-made products of extruded polystyrene foam (XPS) — Specification
TDS pnp_xps300-300TB_600x1250_techcard_en(20.07.2026).pdf (updated 2026-07-22)
DoP DoP PNP XPS 300 EMI_en (U).pdf (updated 2025-10-14)
TDS pnp_xps300W-300WTB_600x1250_techcard_en(20.07.2026).pdf (updated 2026-07-22)
DoP DoP PNP XPS 300 W EMI_en (U).pdf (updated 2025-10-13)
TDS pnp_xps300MG_600x1250_techcard_en (21.07.2023).pdf (updated 2025-03-17)
DoP DoP PNP XPS 300 MG_eng.pdf (updated 2025-03-17)
TDS pnp_xps500-500TB_600x1250_techcard_en(20.07.2026).pdf (updated 2026-07-22)
DoP DoP PNP XPS 500_en (U).pdf (updated 2025-07-22)
TDS pnp_xps700_600x1250_techcard_en (21.07.2023).pdf (updated 2025-03-17)
DoP DoP PNP XPS 700_eng.pdf (updated 2025-03-17)

Frequently asked questions

What does CC(2/1.5/50)130 mean on a PNP XPS data sheet?

It means the board will not deform by more than 2 % of its original thickness when subjected to a sustained compressive stress of 130 kPa, extrapolated over a 50-year service period, as determined by the EN 13164 test method. The stress applied during the test was 1.5 times the ratio used for the short-term compressive strength test.

Is the short-term compressive strength (CS class) enough to select XPS for a permanently loaded floor?

No. The CS class characterises resistance to a load applied over a short duration; for floors under permanent loads you must also check the CC value, which limits long-term creep deformation to 2 % over 50 years. Always verify both figures in the current TDS and DoP, and have a qualified designer confirm the load does not exceed the declared CC limit.

Which PNP XPS products carry a declared compressive creep value?

XPS 300 and XPS 300 W (boards above 30 mm, CC(2/1.5/50)130), XPS 300 MG (CC(2/1.5/50)90), XPS 500 (CC(2/1.5/50)150), and XPS 700 (CC(2/1.5/50)210) all carry declared CC values per EN 13164. Other grades in the range — see the current TDS for those products.

Why does XPS 300 MG have a lower CC value (90 kPa) than XPS 300 (130 kPa) despite the same compressive strength class?

The milled and grooved surface treatment of the MG variant affects the material cross-section available to resist sustained load, which results in a lower declared creep limit. Both products carry the same short-term compressive strength class (CS(10\Y)300), but the long-term creep performance is a separate test result that must be read independently from the TDS.

What level of long-term settlement is considered acceptable under EN 13164?

The CC designation as defined in EN 13164 sets 2 % of original board thickness as the maximum allowable creep deformation over 50 years at the declared sustained stress. Whether that level of settlement is acceptable in a specific assembly depends on the floor finish, tolerance requirements, and applicable national regulations — a determination that requires a qualified designer.

Where can I find the full technical data and Declarations of Performance for PNP XPS floor products?

Technical data sheets and DoPs for all PNP XPS products are available at the documentation page. For project-specific advice, contact the PNP XPS technical team at sales@pnpinsulation.com or through the contact page.