Few additional points...Anthony [OP] specifically asked
not to be referred to a dry suit, but wished wet suit options...of course that was ignored...
Can dry suits be warmer than wet suits in cold water? Of course but that was not what the OP asked.
Post #24 John's mostly says it all for wet suits; like he said you can't dive an open cell wet suit, sponges are open cell....closed cell traps gas for insulation....here are a few added bits for the mix.
In "the day" Rubatex [sp?] wet suit rubber was the best neoprene for wet suits as it was gas blown with nitrogen...why nitrogen cuz:
"Nitrogen is slightly better than air for insulation because it has lower thermal conductivity, meaning it retains heat more efficiently. This is why many high-quality wetsuits are designed with nitrogen-filled neoprene."
I do not know of any neoprene today that is gas blown [how produced] with nitrogen [process was a simulation of explosive DCS to infuse the rubber with nitrogen bubbles].....big deal? Probably not, but the old 'Rubatex' neoprene was a durable, flexible and warm product...long gone. Went through a lot of corn starch!
Another consideration of course when diving a wet suit is the loss of insulation and buoyancy at depth; balanced against the dry suit's hpefully 'constant volume' design and static buoyancy. Issue with going to 8mm or even with my 7mm Farmer John w/14mm over upper body and attached hood is the need to carry a lot of weight to off-set the neoprene buoyancy in shallow and then have sufficient wing/BCD lift at depth when suit compresses...once weights/buoyancy set, no biggee, done deal.
I have owned and used crushed neoprene dry suit [DUI], Uni-Suit, Semi-dry and Viking sheet rubber dry suit and still prefer diving my custom made wet suit even down to or below 40 degree water.... My first dive suit was an Aquala sheet rubber front entry, tie off with surgical rubber, with poor undergarments in Lake Tahoe 40F water in '55. We froze in those suits since the only air pushed into the suit was by blowing into the mask and under the attached hood into the suit; yes, got lots of "monkey bites" from suit compression and ascents could get interesting... Converted to "Dive & Surf"'s Thermocline wet suit in '57 and was much warmer, even on very deep dives in Tahoe.
So to each their own, I prefer the less complicated and less ornate diving with a flexible, custom wet suit.
[PS....Another plus for a wet suit is you don't have to wear a diaper; yes, loss of urine is loss of heat, but damn it can feel good!
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