My Semi dry employs a drysuit neck, wrist and ankle seals as well as a dry suit zipper. It's a 6.5 mil neoprene that acts like a drysuit, but has no valves for air. The seals are set up just like a drysuit and work with the hood boots and gloves to minimize any water entry. Active range is 38 to 70 deg.
Fit on the seals is primary for the suit to work, because it is not like a wetsuit in body fit. There is some space in the suit. You must burb the air out before sealing and the warm water that I use keeps any water leaks at bay for while.
A semi dry is just that. The suit attempts to limit any water in the suit and thus maximize the warmth. If the seals are really good, you will only have your own sweat (another reason why add warm water), as the moisture in the suit.
My suit works very well for me. It's also a far cry from the expense of a drysuit. Please do not get me wrong, a drysuit has a definate purpose if you do a lot of cold water diving. But for me, the semi dry fits all of my current needs.
Enjoy the ride.
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