Determining the mass loss of cellular plastics during combustion provides a direct, quantitative measure of how quickly foam materials decompose, generate combustible fuel, and contribute to fire growth. This technical article explains the measurement principles, relevant international standards, specimen requirements, test procedures, and data interpretation for mass loss testing of foam plastics, supporting manufacturers, researchers, and compliance engineers in material selection, flame-retardant development, and regulatory conformity assessment.
Technical Overview
Mass loss determination is one of the most fundamental and informative measurements in the fire-performance evaluation of cellular plastics (foam plastics). Because foams combine low density, high specific surface area, and large volumes of trapped air or residual blowing agent, they tend to pyrolyze rapidly when exposed to heat, feeding volatile fuel into the flame zone and driving fast fire growth. By continuously recording the mass of a burning specimen on a precision load cell, laboratories can quantify exactly how much material is consumed, how quickly it is consumed, and how much char or inorganic residue remains after the test.
The mass-versus-time curve is also the foundation for calculating the mass loss rate (MLR), which correlates strongly with heat release rate, smoke production, and the release of toxic combustion gases. Modern bench-scale fire test instruments therefore treat gravimetric data not as a supplementary observation but as a primary measurement channel, acquired simultaneously with heat release (oxygen consumption method) and smoke opacity (laser photometry).
- ISO 5660-1 – Reaction-to-fire tests: heat release, smoke production and mass loss rate (cone calorimeter method)
- ASTM E1354 – Heat and visible smoke release rates using a cone calorimeter, including continuous mass measurement
- GB/T 16172 – Chinese national standard for the cone calorimeter method, technically aligned with ISO 5660-1
- ISO 13927 – Simple heat release test using a conical radiator and a thermopile-based mass loss calorimeter
- ASTM E2102 – Measurement of mass loss and ignitability using a mass loss calorimeter
- ISO 11358 – Thermogravimetry of polymers for small-scale decomposition studies
All of these methods are routinely performed by accredited third-party laboratories as part of material qualification, research and development, and regulatory compliance programs for building products, transportation interiors, furniture, and electrical applications.
Testing Samples
Rigid Thermoset Foams
Polyurethane (PU), polyisocyanurate (PIR), and phenolic foams are widely used as thermal insulation in walls, roofs, and sandwich panels. In mass loss testing these materials form a thermally protective char layer, so the mass-loss curve typically shows a prolonged decomposition plateau, and the residual mass fraction is a key indicator of char-forming efficiency and flame-retardant performance.
Thermoplastic Foams
Expanded polystyrene (EPS), extruded polystyrene (XPS), polyethylene (EPE), polypropylene, EVA, and flexible or rigid PVC foams behave very differently. They soften, melt, and often exhibit a sharp, steep mass-loss step near a dominant decomposition temperature, with melt dripping and pool-fire behavior strongly influencing the results. The edge-framing and retainer-frame procedures specified in ISO 5660-1 are used to keep such specimens in place and to ensure reproducible measurements.
Foam-Containing Products and Composite Specimens
Finished articles such as faced insulation boards, upholstered furniture composites (foam plus fabric and interliner), automotive headliners, seat pads, acoustic panels, and protective packaging foams can be tested as layered or assembled specimens, provided the total thickness and construction comply with the applicable standard. Testing the real product build-up is essential because facings, adhesives, and barrier layers substantially alter the mass-loss behavior of the underlying foam.
Specimen Preparation and Conditioning
For cone-calorimeter-type testing, the standard specimen is 100 mm × 100 mm with a thickness of up to 50 mm. The rear face and edges are wrapped in aluminum foil so that molten material remains on the load cell, and specimens are conditioned to equilibrium at 23 °C ± 2 °C and 50 % ± 5 % relative humidity in accordance with ISO 291 or ASTM D618. For thermogravimetric analysis, only a few milligrams of representative material are required.
Testing Items
Depending on the instrument configuration and the selected standard, a mass-loss determination program for cellular plastics typically reports the following parameters:
- Mass loss rate (MLR), expressed in g/s, obtained as the numerical derivative of the mass-versus-time curve
- Peak mass loss rate and the time at which it occurs
- Average mass loss rate over defined periods, such as 60 s, 180 s, or the full test duration
- Total mass loss and percentage mass loss relative to the initial specimen mass
- Residual mass fraction, char yield, and inorganic residue after flaming combustion ceases
- Time to sustained ignition and total burning duration, recorded simultaneously with the mass channel
- When a full cone calorimeter is used: heat release rate (HRR), peak HRR, total heat released, effective heat of combustion, and specific extinction area, all evaluated alongside and normalized against the measured mass loss
For regulated applications, classification indices such as MARHE (maximum average rate of heat emission) used in EN 45545-2 for railway applications, or the heat-release-related criteria embedded in the EN 13501-1 and GB 8624 building classification schemes, are derived from these primary measurements.
Testing Methods
Cone Calorimeter Method (ISO 5660-1 / ASTM E1354 / GB/T 16172)
A horizontally oriented specimen is placed on a load cell with a resolution of about 0.1 g and exposed to a controlled radiant flux from a truncated-cone heater, typically 25, 35, 50, or 75 kW/m². An electric spark igniter pilots the evolved volatiles. Mass is logged continuously, usually at 1 Hz or faster, until the specimen is completely consumed or the mass change falls below a defined threshold. The test yields the complete mass-loss curve, from which MLR, peak MLR, and residual mass are computed, while oxygen-consumption gas analysis provides simultaneous heat release data. This is the reference bench-scale method for reaction-to-fire characterization of foam plastics in most international regulations.
Mass Loss Calorimeter Method (ISO 13927 / ASTM E2102)
The mass loss calorimeter uses the same conical radiator and load-cell arrangement as the cone calorimeter but omits the exhaust gas analysis train, making it a simpler and more economical screening instrument. It measures ignition time and mass loss under identical exposure conditions and is well suited to comparative ranking of foam formulations, flame-retardant loadings, and barrier layers during product development.
Thermogravimetric Analysis (ISO 11358)
TGA measures the mass of a milligram-scale foam sample while it is heated at a controlled rate, commonly 5–20 °C/min, under nitrogen or air. It reveals the onset temperature of decomposition, the temperature of maximum degradation rate, the number of decomposition stages, and the final residue at 600–800 °C. Because it runs under well-defined atmospheres with negligible heat-transfer limitations, TGA is the preferred tool for mechanistic studies of flame-retardant action, such as char promotion by phosphorus additives or intumescent systems, although its results cannot be transferred directly to real-scale fire behavior.
Chamber and Tube-Furnace Methods with Auxiliary Mass Recording
Smoke-density chambers operated per ISO 5659-2 and steady-flow tube furnaces operated per ISO/TS 19700 frequently incorporate specimen weighing as an auxiliary channel. These methods correlate mass loss with smoke optical density or toxic gas yields, supporting fire-hazard engineering assessments for transportation and building applications, including the FTP Code requirements for shipboard materials.
Applications
- Building insulation: classification of EPS, XPS, PU/PIR, and phenolic foam boards under EN 13501-1 and GB 8624, where combustion behavior determines the fire classification class
- Railway vehicles: EN 45545-2 requirements for interior foams and seat components, which rely on cone calorimeter data including mass-loss-derived indices
- Marine and offshore: qualification of cabin linings, bulkhead insulation, and upholstered furnishings against international fire test procedure codes
- Automotive and aviation: development of seat foams, headliners, and trim materials with reduced burning rate and dripping tendency
- Furniture and mattresses: barrier and interliner evaluation, where a reduced mass loss rate directly lowers full-scale fire hazard
- Research and development: screening of halogen-free flame retardants, intumescent coatings, expandable graphite, and nanocomposite additives in PU and PS foams
- Quality control: batch-to-batch verification of flame-retardant loading and foam formulation consistency
- Fire-safety engineering: use of measured MLR curves as input data for zone and CFD fire models in performance-based design
FAQ
Why is continuous mass loss measurement more useful than simply weighing ash residues?
Residue weighing only gives the final state. Continuous gravimetry captures the entire decomposition history, including the rate of fuel release that drives flame spread and heat release. The rate information is what correlates with real fire hazard and what fire models require as input.
What heat flux level should be selected for foam testing?
Common practice is 35 kW/m² for general screening and 50 kW/m² to simulate developed-fire exposure; lower fluxes such as 25 kW/m² approximate early-fire conditions. For thermally thin, highly combustible foams such as EPS, the lowest stable flux consistent with the relevant regulation is often preferred to avoid unrealistically violent degradation.
How are melting and dripping handled?
Specimens are wrapped in aluminum foil and, for thermoplastics, may be tested in a retainer frame so that melt remains on the load cell. This ensures that mass removed from the specimen is genuinely converted to gas-phase fuel rather than merely relocated.
Can TGA results replace cone calorimeter mass loss data?
No. TGA operates on milligram samples at controlled heating rates without flaming combustion, so it identifies decomposition chemistry but not flaming behavior. Regulatory classifications rely on cone-calorimeter-type measurements, while TGA supports formulation development and mechanistic interpretation.
What does a low residual mass indicate?
A very low residue fraction means almost complete gasification of the polymer into combustible volatiles, which is typical of untreated hydrocarbon foams and implies high potential heat release. A high residue or char yield indicates thermally protective char formation, generally beneficial for insulation performance and structural integrity in fire.
How long does a typical test take?
A single cone calorimeter run, including specimen mounting and system stabilization, typically takes 20 to 45 minutes depending on material thickness and burning duration, while TGA experiments take one to three hours. Accredited third-party laboratories usually report validated results within five to ten working days after specimen conditioning.