Present industrial development of the civilization requires a significant amount of energyEnergy and the main source is currently burning of fossil fuels. The consequence of this approach is that huge amounts of waste gases (mainly carbon-dioxide) are emitted which significantly influences the environment. Powders of inorganic zeolites in combination with polyethylene oxide matrix have been observed to form compositeComposites material which is suitable for making membranes with good separation properties for carbon-dioxide. In previous works, it has been shown that those membranes show good properties in acceptable range of gas compositions and temperatures. The influence of the thickness of the membrane has been tested in experiments in order to determine optimal thickness of the membrane for this purpose.