Yes, semi-drys. A silly name, but we've been through that. I used to do weekend dive trips out of southern England, usually leaving dock pretty early (timing was tide dependent) and travelling for a couple of hours to the first dive site. Then lunch on board followed by a second dive. I only ever did those trips in a drysuit, as did most of the other divers. There were a few hardy souls who in summer insisted on using a semi-dry. I did these trips 8 or 10 times every summer for years, and in all that time I never knew a diver who had used a semi-dry for the first dive to make the second dive - they'd lost too much body heat.
Semi-drys are useful in that they don't contain air so buoyancy control is much simpler than with a drysuit. This is why some people use them. For me I've never seen the point, nor in having especially thick wetsuits either. If I need more than a 5mm well fitting wetsuit then I wear a drysuit, every time. I even see people here in Belize (water temp currently 85f) wearing drysuits, when I'm diving alongside them in shorts and rashguard!
