Room temperature changes how well you think. In a controlled test, 25 participants read an 800-word essay and answer 10 questions on three separate days — once at 20°C, once at 25°C, and once at 30°C. Each day uses a different essay of equal difficulty, and an English teacher grades all the tests. Comparing average scores across the three temperatures reveals the range where reading comprehension peaks and where rising heat begins to impair mental performance.