Heated car seats are nice and toasty for your bottom, but it may prove be too toasty for men's sperms:
Optimal sperm production requires a temperature 1 to 2 °C below
the core body temperature of 37 °C. This is one reason why the testicles hang outside the main part of the body. To test whether heated car seats might be raising scrotal temperatures above this threshold, Andreas Jung at the University of Giessen in Germany and his colleagues fitted temperature sensors to the scrotums of 30 healthy men, who then sat on a heated car seat for 90 minutes.
An hour in, and scrotal temperature had already risen to an average of 37.3 °C, with a maximum temperature in one man of 39.7 °C. [...] Although that's only a slight increase due to the heated seats, Jung notes that it may nevertheless be enough to damage the sperm production process.