I work outdoors for a living, and it is particularly cold this winter. I typically wear thermal bottoms and a thermal shirt as underwear. I thought I would kick it old school and try a union suit. So far, I am completely not impressed. The fabric of this particular union suit does not hold heat nearly as well as my other thermals. I noticed a significant difference, and I do not stay warm while wearing these outdoors. The butt-flap is incredibly difficult - the button/button hole are both very small. Without being too crass or descriptive: I save more time by unbuttoning the union suit entirely and dropping trou, than I do using the butt-flap. So far, this particular union suit is more inconvenient than functional.