In colder weather it's all about managing sweat. As everyone has mentioned so far nothing is truly breathable, it is a dream that some day may be realized but not yet. Any jacket you buy is a compromise in some way. Schoeller soft shell fabrics are really pretty darn good as far as regulating sweat and breathing, but if it's pouring rain, no. It's all about you, your tolerance, your prevailing conditions, your budget and it varies for everyone. You can find pieces that work well for you most of the time, but rest assured they are all a compromise in one way or another.