Since increasing energy costs and uncertainty within the energy sector represent a threat for the sustainability of greenhouses, researchers are conducting extensive studies on the subject of energy conservation. Thermal curtains, which are finding increased use in recent years for energy conservation purposes, play an important role in energy saving. This study investigates the effect on greenhouse temperature of thermal curtains used in both heated and unheated plastic and glass greenhouses in the Cukurova region, which has a Mediterranean climate, and the level of fuel saving ensured by thermal curtains used in heated greenhouses. Measurements were made on different days of the production cycle. The study results indicated that the use of thermal curtains leads to a temperature difference of 3 K in unheated glass greenhouses and of 2 K in unheated plastic greenhouses. It was observed that imported LS 17 thermal curtains ensured a 63% fuel saving in heated glass greenhouses, while white thermal curtains produced in Turkey and consisting of tightly woven polyethylene ensured 36% fuel saving in heated glass greenhouses.