Determination of water vapor resistance with the Empa double chamber method

The “double chamber method” is used to measure the water vapor transmission rate at defined partial pressure differences by exposing the sample to two different climates concurrently. It allows the determination of water vapor resistance at different environmental conditions, simulating conditions similar to real use.

Test description

The pre-conditioned, round sample (60 mm in diameter) is sealed at the rim with a ring of aluminium foil and attached tightly to the opening of the smaller chamber. The water reservoir to maintain the climat in the smaller chamber is monitored by a balance. The supplied water is monitored by a computer program reading the balance weight over time.

Principle of the measurement of the WVTR with the double chamber method (DCM)

This setup is placed in larger climatic chamber which is set to a different climate. A ventilator at the outer surface of the smaller chamber ensures that there is a constant air exchange. Water vapor is transported through the sample depending on the water vapor pressure difference defined by the two different climates on the inside and outside of the sample and the properties of the sample.

The steady state of moisture exchange is a measure of the water vapor permeability of the tested sample at the set conditions, for example winter (Climatic chamber 5°C/50% rh, Optical 20°C/50%rh) or summer (Climatic chamber 27C/50% rh, Optical 35°C/70%rh)

Measurement setup
Test conditions

laboratory scale, computer, climatic chamber, integrated humidity calibrator (Optical), datalogger (MSR 145)

Number of samples

Sample diameter
60 mm

Orientation of sample
outerside towards cliamtic chamber

Measurement time
according to client

Climates (examples)
winter (climatic chamber 5°C/50% rh, Optical 20°C/50%rh)
summer (climatic chamber 27°C/50% rh, Optical 35°C/70%rh)


If you have any queries regarding the suitability, cost or time frames associated with this testing, please do not hesitate to contact us.