I'm going to agree that semi-dry is a marketing term. I dive in a Mares Isotherm 'Semi-Dry' suit. I did alot of research before purchsing this suit and believed it to be the best 'semi-dry' on the market. The difference between this and, for example, my dive buddies Parkway 7mm wetsuit is the zipper and the extremity opeinings. The zipper is a standard drysuit zipper. It is a excellent seal, but has all of the disadvantages of a dry suit zipper (maintainance, PIA location, and hard to operate). The extremity openings all feature rubber seals approx 6" long. These seals get folded underneath itself. The boot, glove, hood then goes on top of the runner and a neoprene sleeve zippers closed on top. I bought the matching mares boots which are supposed to also be 'semi-dry'. My findings are as follows... the suit stays as dry as a dry suit, allowing almost zero water to enter. The boots get some water in them, not perfect. A little duct tape might fix that though? The challenge is getting the suit on and off as the seals are VERY tight (key to dry) and bleeding out the air. Unlike a dry suit where you keep an airspace inbetween, the semi-dry is worn tight like a wetsuit. Air trapped is bad for bouyancy and seals. Upon entering the water you must careful submerge to your neck and bleed the air out of the neck. This is easy in still water beach dives but a major challenge in rough water on a boat dive. All in all, the semi-dry is the way to go in my opinion. It is much more comfortable than a wetsuit, very warm and has none of the hassles of a full dry suit. The cost was pretty reasonable too. I dove this weekend in low 50 deg water and was warm! not even the slightest hint of chill. I have also used it into the 70's with out gloves and a hood and was still confortable when my buddy was dyign hot in his 7mm wet. The dry seems to allow a wider comfort range for temp too. Anyway, thats my 2 cents worth. Email me if you have questions. P.S. the fit is 10x more critical in any dry type suit so make sure it is very tight around the extremities or it will be a semi-wet!