This applied study focuses on evaluating the effectiveness of several thermal insulators on the thermal performance of buildings in the city of Riyadh in the central region of Saudi Arabia. Typical models equipped with different types of thermal insulators in their walls were used in this study. The experiment was conducted at the Research Station of the College of Architecture and Planning on King Saud University Campus in Riyadh. The study aims to know the effect of a number of modern artificial insulation materials commonly used in the insulation of buildings in the Kingdom as well as some natural materials available at construction sites on the thermal performance of buildings. The study used a number of thermal insulators manufactured and commonly used in the city of Riyadh, such as glass wool, perlite and polystyrene. A number of cheap natural materials well known in the traditional architecture of their good thermal properties and available on most construction sites or near them such as mud, sand and mixture of these two materials were also examined. The experiment was conducted in the winter season and the summer season of the same year, where readings were taken for the months of December and August to represent the two seasons respectively. Readings of indoor air temperatures were collected and analyzed and presented. The results of the study concluded that the use of a mixture of sand and mud is effective when used in the insulation of the external double walls. It was also revealed that the rest of the artificial and natural insulation materials used in the experiment were very close in their performance. The study concludes with some appropriate architectural recommendations for the possibility of using the mixture of soil and sand to achieve acceptable thermal insulation as well as economical benefits for buildings in the city of Riyadh and similar areas of the desert climates.