Graham Thompson from Trail magazine, in conjunction with Leeds University, has extensively studied the build up of humidity in boots with membranes compared to those without. Some of the conclusions relate just as well to clothing:
- People sweat to different degrees
- Breathability depends on the temperature gradient
- Membranes impede drying
- Membranes reduce breathability and usually increase humidity and temperature inside
More commentary on this can be seen at Outdoors Magic.