News Article

Evaluation of initial thermal conductivity of polyurethane rigid foam formulated with 4th generation blowing agents.

David Boote
Technical Manager
(In-situ foams & Quality)
Isothane Ltd,
Newhouse Road,
Huncoat Business Park,
Accrington, Lancashire.
United Kingdom


Fourth generation blowing agents described as hydrofluoroolefins (HFOs) are coming on the market as replacements for the current hydrofluorocarbon (HFC) group of products.

The current HFC blowing agents are being phased out due to their relatively high global warming potential (GWP). Under the new F gas regulations HFCs will no longer be able to be used in Europe after 2023.

The new HFO products have significantly lower GWP values than HFCs but maintain the thermal insulation performance characteristics of their predecessors.

Due to the phase out of the blowing agents now used, there is a requirement to reformulate existing rigid foam systems.


Isothane Ltd has a range of rigid polyurethane foam systems based on the 3rd generation blowing agents or HFCs. The foam systems are developed for in-situ on site application, where the products are supplied as two components, a resin blend and an isocyanate. The two components are then processed using specially designed machinery to either spray or dispense the finished foam product.

The thermal performance of polyurethane foam systems is determined according to the test methods in BS EN 14315-1 “Thermal insulating products for buildings – In-situ formed sprayed rigid polyurethane (PUR) and polyisocyanurate (PIR) foam products” and BS EN 14318-1 “Thermal insulating products for buildings – In-situ formed dispensed rigid polyurethane (PUR) and polyisocyanurate (PIR) foam products”. The test methods require the use of a calibrated heat flow meter (HFM) to measure the thermal conductivity of cured foam samples. The initial thermal conductivity value is measured on samples between one and eight days after production.

For Isothane’s current HFC based products the initial thermal conductivity value is measured for every batch produced. Using these results it is possible to compare the initial thermal conductivity of new HFO based formulations.

Due to the physical characteristics of the HFO blowing agent it should be possible to formulate systems containing less blowing agent than the equivalent HFC product.

Spray Foam Systems Specifications

Duratherm (HFC) Duratherm (HFO)
Blowing Agent Level* 100% Blowing Agent Level* 95%
Cream Time 3-5 Seconds Cream Time 3-5 Seconds
Rise Time 20-30 Seconds Rise time 20-30 Seconds
Density 26-30 kg/m3 Density  26-32 kg/m3
Resin Viscosity 270-370 cPs @ 25ºC Resin Viscosity 250-350 cPs @ 25ºC
Resin Specific Gravity 1.13-1.20 Resin Specific Gravity 1.13-1.23
*Compared to standard HFC formulation levels



Five experimental spray foam resin samples were produced using the HFO blowing agent.

These resin samples were then processed through a Gusmer A-25 two component sprayfoam machine to produce cured foam sheets measuring approximately 1000 mm by 700 mm with a thickness of around 80 mm. The sprayed sheets were allowed to condition for 24 hours before specimens measuring 600 x 600 x 50 mm were cut from them. One specimen was produced for each resin batch.

The thermal conductivity of each specimen was then measured using a Fox 600 heat flow meter at a mean temperature of 10°C.

The procedure was repeated with resin samples made to a HFC formulation.

HFO based Samples.

Sample Number 1 2 3 4 5

Foam Core Density (kg/m3)

36.5 36.5 36.5 36.5 36.5
Mean Temperature (°C) 10 10 10 10 10
Upper Plate Temperature (°C) 0
Lower Plate Temperature (°C) 20 20 20 20 20
Initial Thermal Conductivity (W/mK) 0.0187 0.0192 0.0189 0.0187 0.0190
Thermal Resistance at 50mm (m2K/W)  2.67 2.60 2.65 2.67 2.63


HFC based Samples.

Sample Number 1 2 3 4 5

Foam Core Density (kg/m3)

36.5 36.5 36.5 36.5 36.5
Mean Temperature (°C) 10 10 10 10 10
Upper Plate Temperature (°C) 0
Lower Plate Temperature (°C) 20 20 20 20 20
Initial Thermal Conductivity (W/mK) 0.0201 0.0197 0.0199 0.0198 0.0198
Thermal Resistance at 50mm (m2K/W)  2.49 2.54 2.51 2.53 2.53


Thermal Conductivity



The foam samples made with HFO blowing agent had a lower average initial conductivity value compared to foam samples made with HFC. Both formulations produced cured foam with similar physical properties within the required specifications.


Duratherm spray foam samples made using 4th generation HFO blowing agent produced good cured foam, comparable with product made using HFCs. The foam made with HFO had improved initial thermal conductivity values compared with the standard HFC product and required a lower blowing agent addition to the resin formulation.


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