Rob
Being overweight or not is not the cause of the problem. I had heat rash and chaffing problems since High School 30+ years ago. I was not overweight then, though some would consider me as overweight now at 6'2" 220 lbs.

Our bodies are NOT made the same, proportionally, or chemically, so we can all have these problems.

There are also enviornmental conditions to account for. The US is quite diverse in this also, and the different climate zones and humidity changes throughout our country also play into this.

Since I found Body Glide (Which I use daily, kilted or not) I have not had any of the heat rash and chaffing problem.

The problem lies in the generalization, not in the opinion.