I have been putting in some long in water days with the XM450. At first blush, when i pulled it out of the box and went for a dive, it felt like i made a big mistake as it was like wearing cardboard, albeit really really really warm cardboard. They were simply too warm. I actually did a couple dives on them and threw them in the closet next to the 400g's. Then winter rolled around and my powerstretch even with 100g under it just wasn't cutting it anymore, so i dug em out. After a dozen or so dives, it's softened up very nicely... It is now my undergarment of choice. I worried that i would feel the panels, I think I notice them when i first get in the water on my knees, but after an hour with a partially flooded suit i did not notice an appreciable difference between the stretchy part and thinsulate part.