Our thermoplastic polyurethanes (TPU) are permeable to gases and liquids. Different grades, building blocks and additives can be used to meet specific permeability requirements.
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Thermoplastic polyurethanes
Permeability describes the transmission of a medium, usually of a gas, sometimes of a liquid, through a test specimen. The test process for permeability can be divided into three separate stages:
• Entrance of the medium into the test specimen
• Diffusion of the medium through the test specimen
• Escape of the medium from the test specimen

Permeability is directly proportional to the temperature of a test specimen and inversely proportional to the wall thickness. Below you can find an overview of permeability properties for our main TPU materials for different types of gases and fuels. 

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Gas permeability

The following table shows the permeability of different gases for some important Desmopan® grades, measured according to DIN 53380, Part 1, for films with a 100 µm thickness.

Table 1: Gas Permeability G in cm3 / m2 x d x bar
Thermoplastic polyurethanes (TPU) are not generally used as barrier materials. However, polyester TPUs tend to have a lower gas permeability than polyether TPUs, making them more suitable as a barrier material. Additives can also be used to achieve a further reduction in gas permeability. When compounded into the material, they can reduce gas permeability by approximately 30%. If high gas permeability is requested, either polyether-based TPU or a special polycarbonate-based TPU are more suitable choices. The latter category of TPU is especially interesting when increased gas permeability must be combined with resistance to a wide range of chemical substances.

Fuel permeability

The following table shows the fuel permeability (FD) of Desmopan® 786. The measurements were taken according to DIN 53532 on a polyester fabric coated on both sides with a 100 µm layer of Desmopan® 786 and exposed to three different fuels.
Table 2: Fuel permeability in g / m2 / d
Fuel 1 = pure isooctane (2,2,4-Trimethylpentane)
Fuel 2 = blend of isooctane/toluene (70:30 vol.%)
Fuel FAM = blend of pure toluene/isooctane/diisobutylene/pure ethanol (50:30:15:5 vol.%)

Desmopan® 786 is a thermoplastic polyurethane (TPU) containing polyether carbonate polyols. It is well-suited for simultaneous contact with fuel and water. Due to the unique formulation of Desmopan® 786, it offers an equally high resistance against fuels and hydrolysis.

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