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ISO 29470:2020 — Thermal Insulating Products — Determination of the Apparent Density
Standardised bulk density measurement for building insulation materials
Purpose and Scope of Apparent Density Determination
ISO 29470:2020 specifies a method for determining the apparent density of full-size thermal insulating products. Apparent density (often referred to as bulk density) is a fundamental physical property that correlates directly with thermal conductivity, mechanical strength, and material cost. In the insulation industry, density is both a quality control parameter and a design input for thermal performance calculations.
For mineral wool products, a 10 % increase in density typically reduces thermal conductivity by 3–5 % — but beyond an optimal density range, further densification provides diminishing returns and adds unnecessary cost.
The principle is simple: the apparent density is calculated as the ratio of the mass of the test specimen to its volume. However, the standard carefully specifies conditioning requirements, dimensional measurement methods, and calculation rules to ensure reproducible results across different laboratories and product types.
Test Procedure
| Step | Description |
|---|---|
| Conditioning | Minimum 6 h at 23 ± 5 °C; dispute: 23 ± 2 °C, 50 ± 5 % RH |
| Weighing | Balance with accuracy of ± 0.5 % of specimen mass |
| Volume determination | From length, width, and thickness per ISO 29465 and ISO 29466 |
| Calculation | ρa = m / V, expressed in kg/m³ |
The specimen must be the full-size product unless the product standard specifies otherwise. For large products, representative portions may be used if agreed between parties. The standard requires measurement of linear dimensions in accordance with ISO 29465 (length and width) and ISO 29466 (thickness), creating an integrated dimensional measurement framework.
Products with facings, coatings, or integral skins must be weighed including these layers, as they form part of the delivered product. However, if the product standard specifies density of the core material alone, the facings should be removed before measurement.
Engineering Significance and Applications
Density is one of the primary variables under the manufacturer’s control that influences insulation performance. For foamed plastics (PUR, PIR, XPS, PF), density affects both thermal conductivity (through cell structure) and mechanical properties. For fibrous materials (mineral wool, glass wool), density determines the fibre packing factor and thus the conductive-radiative heat transfer balance.
Apparent density is also used as the basis for calculating other material properties such as specific heat capacity per unit volume and for quality control in production: deviations from target density indicate process variations in foam rise, fibre deposition, or compression during manufacture.
In building energy modelling software, insulation density is required input for calculating thermal mass effects and dynamic heat transfer. Accurate density data improves the reliability of annual energy performance simulations.
The 2020 edition (second edition) changed the title from “apparent bulk density” to “apparent density”, updated conditioning requirements, and made editorial revisions.
The apparent density of thermal insulation products is not merely a quality control parameter — it is directly linked to both thermal and mechanical performance. For a given insulation material family, thermal conductivity typically decreases with increasing density up to an optimal point, beyond which solid conduction through the denser matrix begins to offset the gains from reduced radiative transfer. For mineral wool products, this optimum typically occurs at 60–120 kg/m³ depending on fibre diameter and orientation. For foamed plastics, the optimum density range is generally 28–45 kg/m³ for polyurethane and 25–35 kg/m³ for extruded polystyrene. Accurate apparent density measurement according to ISO 29470 therefore serves as both a production quality check and a design input for thermal performance optimisation.
Frequently Asked Questions
Q: What is the difference between apparent density and true density?
A: Apparent density (bulk density) includes the volume of internal pores and voids within the material structure. True density excludes pore volume. For insulation materials, apparent density is always less than true density due to the intentionally porous structure.
A: Apparent density (bulk density) includes the volume of internal pores and voids within the material structure. True density excludes pore volume. For insulation materials, apparent density is always less than true density due to the intentionally porous structure.
Q: How does moisture content affect apparent density measurement?
A: Moisture adds mass and can cause dimensional changes, leading to inaccurate density values. Conditioning to equilibrium moisture content at specified temperature and humidity conditions is essential for reproducible results.
A: Moisture adds mass and can cause dimensional changes, leading to inaccurate density values. Conditioning to equilibrium moisture content at specified temperature and humidity conditions is essential for reproducible results.
Q: Can density be measured on small cut specimens?
A: The preferred specimen is the full-size product. If representative portions are used, they must be agreed between parties and should be large enough to represent the product’s structural heterogeneity (typically minimum 100 mm × 100 mm).
A: The preferred specimen is the full-size product. If representative portions are used, they must be agreed between parties and should be large enough to represent the product’s structural heterogeneity (typically minimum 100 mm × 100 mm).
Q: What changed from the 2008 edition?
A: The 2020 edition changed the title, updated the conditioning clauses to align with other ISO/TC 163 standards, and made editorial corrections. The measurement principle and procedure remain unchanged.
A: The 2020 edition changed the title, updated the conditioning clauses to align with other ISO/TC 163 standards, and made editorial corrections. The measurement principle and procedure remain unchanged.
