Background: For species-appropriate enclosure design, one must understand the thermal comfort of the animal. Aim: This study's goal is to determine whether enclosure areas used by African lions ('Panthera leo') and Siberian tigers ('Panthera tigris altaica') can be predicted by microclimatic conditions in summer months. Methods: 1) To observe each subject's behaviour and use of its enclosure 2) To measure onsite microclimatic parameters 3) To investigate the relationship between the animals' behaviour and their enclosures' microclimate 4) To develop design guidelines. Results: The subjects spent most of the day lying down. On Sunny Days all individuals used Shade more than Sun, while on Indistinct Days Sun was used more than Shade. A gradient of shade is essential in enclosure design. A water pool is a valuable resource for tigers. Conclusions: Discussion of energy budgets, substrate, shade source, topography and water shows how to maximize thermally comfortable spaces for zoo felids.