Characteristics of Rigid Polyurethane Foam

This is fundamental for all applications. Performance must be guaranteed under actual operating conditions (temperature and relative humidity); furthermore, the stability of the material and its insulating effectiveness must be ensured for the entire lifespan of the building structure.

Thermal conductivity (λ) is the amount of heat that passes through one square metre of a material, with a thickness of one metre, when the temperature difference between the two sides is one degree. Therefore, the lower the λ value, the greater the insulating power of the material.
Products subject to CE marking display the λ_D value on their label. This corresponds to the average value over 25 years of service, applicable to 90% of production with a 90% statistical confidence level, evaluated at a test temperature of 10 °C and expressed in the International System unit: W/m⋅K

For all insulation materials subject to CE marking, the design thermal conductivity (λ_U) matches the declared thermal conductivity (λ_D) under standard operating conditions (temperatures between 0 and 20 °C and Relative Humidity between 0 and 50%).
Only if the temperature and relative humidity ranges differ substantially from standard conditions can the specifier adjust the declared thermal conductivity values of any insulation material using the BS EN ISO 10456 standard.

Declared thermal transmittance or thermal conductance (U_D)
This is the ratio between the thermal conductivity λ_D and the thickness of the insulation used (d, expressed in metres).
U_D = λ_D / d
unit of measurement: W/mqK
Low transmittance values correspond to high thermal insulation values. Transmittance is the inverse of thermal resistance (U = 1/R).

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Thermal resistance (R_D)
This is the ratio between the thickness of the insulation used (d, expressed in metres) and the declared thermal conductivity λ_D.
R_D = d / λ_D
unit of measurement m²K/W
It represents the structure's ability to resist the transfer of heat; obviously, the higher this value, the greater the insulating capacity of the material. Thermal resistance is the inverse of transmittance (R = 1/U)

Designation code WL(T)
Water is an excellent thermal conductor and it is therefore important that insulating materials are unable to absorb it. The foam used in STIFERITE panels has a closed-cell structure, making it impervious to water. A small amount of water absorption may occur only at the edge of the panel, where the foam has been cut, or at the surface layers, depending on their hygroscopicity or impermeability.
Due to their waterproof properties, the water absorption of STIFERITE products is assessed by immersion in accordance with the particularly stringent conditions of standard EN 12087, which requires measurements to be taken after the test specimen has been fully immersed for 28 days.

Designation code WS(P)
Most insulating materials, particularly those of a fibrous nature, are assessed solely for water absorption by diffusion following partial immersion of the test specimen for 24 hours, as stipulated by standard EN 1609. Under these test conditions, the water absorption of STIFERITE foams is negligible; whereas it is modest for products coated with hygroscopic materials (paper and cardboard).

Designation code Z o MU
Polyurethane foam, without facings, is permeable to vapour (water vapour diffusion resistance factor, μ≤10). Thanks to the wide range of available facings, STIFERITE panels can offer either vapour permeability or impermeability performance, depending on specific application requirements. In some structures, vapour permeability is useful to allow a steady flow of vapour between the interior and exterior. In other types of applications—for example, in environments with high humidity percentages or steep temperature differences—it may be necessary to install a vapour barrier on the warm side of the structure and/or use low-permeability insulation materials to act as a vapour check.
Since STIFERITE panels are composite products made of different materials, their labels display the water vapour resistance value (Z) alongside the more commonly used water vapour diffusion resistance factor (μ).

Designation code DS(TH)i
The dimensional stability of an insulation material is an important characteristic for many applications. It is critical for roofing applications—under exposed waterproofing membranes—and in External Wall Insulation (EWI) systems, which represent one of the primary uses for STIFERITE panels. It can be defined as a material's capacity to maintain its original shape and dimensions over time and under varying operating conditions. This is determined by measuring the dimensional changes (linear and thickness) experienced by a test specimen subjected to specific temperature and humidity conditions for a set duration (EN 1604). Each product standard considers the temperature (T) and humidity (H) conditions deemed critical for that specific material. Therefore, for comparative assessments between different materials, it is important to verify that the testing conditions are identical. The performance of individual STIFERITE panels varies depending on the type of facing and the thickness used (see Technical Data Sheets). Generally, the best stability performance is found in panels with inorganic facings (glass fibres, aluminium, etc.) which, unlike paper-based facings, are unaffected by changes in humidity.

Unlike other plastic insulating materials, STIFERITE foams can be used across a very wide temperature range, from -40 to +120°C; they are therefore particularly suitable for all applications involving significant temperature fluctuations, such as, for example, roofing beneath exposed prefabricated waterproof membranes or external wall insulation systems. For short periods, temperatures of up to +200°C can be tolerated without any reduction in performance.

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The types of panel intended for roofing applications are compatible with flame-welding of waterproofing membranes and with bonding using hot-melt adhesives.

For insulation materials subject to CE marking, fire reaction performance is assessed in accordance with the Euroclass system (EN 13501), which is based on a combination of various harmonised tests (EN 11925-2, EN 13823).
The system comprises seven classes, designated by letters:
           • A1 and A2: non-combustible inorganic materials
           • B, C, D, E: combustible organic materials with varying fire reaction performance
           • F: combustible materials that do not meet Class E criteria
For some classes, the assessment of additional parameters is also required, such as smoke development (s) and the droplet formation of burning particles (d).
For rigid polyurethane foam products, the Euroclass fire reaction rating varies, depending on the type of foam and the nature of the coatings, from Class F (for panels with paper or bituminous coatings) up to Class E or D. Higher classes, up to B, can be achieved with specialised foams and metallic or inorganic coatings, such as, for example, the STIFERITE panels from the RP and Fire B series.
The harmonised standards for insulation products provide for the possibility of assessing the fire reaction of products under actual conditions of use ('end-use conditions'); the tests carried out confirm the good in-situ performance of STIFERITE panels, which easily achieve the highest classes, B s2 d0 and B s1 d0, specified for organic insulation materials.

Designation cod CS(10/Y)
Compressive strength is the stress that an insulation material is capable of withstanding when subjected to a compressive force applied, at a set speed, in a direction perpendicular to the main faces of a square test specimen. The reference standard is EN 826, and the measured compressive strength values are expressed in kPa.
CE marking requires the indication of the value determined at 10% deformation (relative deformation). For STIFERITE panels, this performance varies depending on the type of facing and the thickness considered (see Technical Data Sheets).
The performance range for standard panels is between a minimum of 100 kPa and a maximum of 200 kPa.

Designation code CC(i1/i2/Y)σ_c
The compressive strength at 10 per cent compression is indicative of a material's performance when subjected to an instantaneous load. To assess the behaviour of materials subjected to continuous loads, whether static or dynamic, and to correctly dimension flooring, the test method described in standard EN 1606 is used, which involves evaluating the maximum load that can be applied over 10, 25 or 50 years (y) of service, subject to a maximum deformation of 2 per cent.
The performance characteristics of the STIFERITE range are suitable for supporting flooring or roofing subjected to very heavy static and dynamic loads, such as, for example, cold store floors and drive-over roofs.
The magnitude of the anticipated loads will determine the correct dimensioning of the floor thickness and/or reinforcement. Recent tests carried out at the University of Padua, Department of Civil, Construction and Environmental Engineering, have demonstrated the suitability of STIFERITE panels for long-span structures, inter-storey slabs, ground-level slabs and drive-over slabs.

Noise propagation depends on the interaction of numerous variables, which makes the phenomenon particularly complex. In the building industry, meeting acoustic comfort requirements depends not so much on the individual materials used as on the composition of the entire structures and their flawless on-site construction.
STIFERITE panels are lightweight and therefore do not contribute significantly to the mass of structures; as is well known, mass is the primary parameter for acoustic insulation in monolithic structures. Nevertheless, recent research and laboratory analyses, carried out on moderately lightweight building structures, have shown that STIFERITE thermal insulation performs well, including in terms of acoustic protection, depending on the specific layered construction under consideration.
The test programme carried out in 2009 at notified laboratories assessed the acoustic performance of various layered configurations of masonry walls and lightweight roofs on timber structures; the performance data were compiled and analysed in a specific Technical Report entitled "Sound Insulation – A New Perspective". All tests were carried out in accordance with the most recent Guidelines, which stipulate specific precautions such as:
- allowing the sample to stabilise before testing, in order to eliminate the 'moist mass' which contributes
– obviously only temporarily
– to acoustic performance,
- the assessment of the attenuation of samples placed horizontally rather than, as is often the case, vertically.
Laboratory tests have confirmed that, due to the effect of the weight of the sample, the data obtained from vertical test specimens are 4–7 dB better than those obtained from horizontal test specimens.
Therefore, when making comparative assessments of the provided laboratory certificates, it is important to carefully verify that the described testing conditions are consistent.