These aren't quite a "loose" fitting jean. I normally wear Levi's 569's in 32x30. I bought the Carhartt's in 33x30 and they fit about the same as the Levi's with 10 minutes of break-in. One important thing to note is the Carhartt's don't really loosen up as you wear them. The Carhartt's are also about 1" longer than my Levi's. They are a little stiffer than most jeans only because they haven't had 1/2 their life washed away at the factory; which I think is a good thing. These Dungarees are comfortable enough to lounge around the house in, too.
Don't expect the flannel to be thick like some puffy ski pants. These Dungarees are built for function, allowing you to move... it's a lightweight flannel; just enough to keep the wind out, and keep you warm when you're working in the cold.
I anticipate getting at least half a dozen(probably more) winters of heavy use out of these pants. And I will be buying more. So should you.