The purpose of diploma thesis was to find out the proper parameters for welding of polyethylene foil on road sheet. We were also researching how different thickness of foil, between 100 microns and 400 microns, influence on process of welding. The ultrasonic welding was made with titan sonotrode with shape of teeth and different welding parameters such as time of welding, power of welding and force of welding. The purpose of welding was to get rid of contamination of surrounding liquids. The quality of weld was made with pressure test. We figure out that in process of welding the important role is also the flatness of sheet. The resistance of weld on pressure test was better endured with thicker foil 400 microns, so it is more proper that 100 microns thin foil.