Buffalo is all I use--South Dakota to Florida. In NW Florida we get below freezing temps, often with very high relative humidity. It's all about the right weight. And, yes, you do have to vent at times--thus the reason they provide ample venting options. Read what Buffalo says on its site about WHY the system works. It is accurate. The materials used do what they say they will do. No fabric is 100% breathable (or really even close to it)--that would defy the laws of physics. Buffalo allows you to manage the water that is going to escape from your body in the form of sweat. Brynje helps that with its own theory of use (trapping air to warm you--which Sitka is pushing now with it's new Aerogel infused products). And, yes, I know that Buffalo says to wear "next to skin". Brynje is a modification I choose because it works for me, and it's still pretty darn close to next to skin.