The impermeabilization of final cover layer of any municipal solid waste landfill (MSWL) is considered an important matter in reducing rain water infiltration as well as gas flow generated by waste organic matter decomposition process. Landfill gas (LFG) liberation may cause a number of environmental impacts, basically due to the presence of methane and carbon dioxide in its composition. An extensive program of laboratory and field tests were carried out in order to investigate the properties of the final cover layer at two municipal solid waste facilities in Recife-PE, Brazil. This paper presents experimental techniques developed to study gas flow through unsaturated soils. These studies included the use of a laboratory permeameter as well as the development of a simple device for field tests. The results allowed to determine the air permeability parameters and estimate of LFG flow to the atmosphere