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"I have some experience that might be contentious. I've been certified a year. Done 16 dives [as a certified diver]. 7 in Monterey the rest in the tropics. Of the 7 in Monterey: 2 dives in a dry suit with a 200 undergarment for my PADI dry suit diver specialty cert at 49-55deg and 4 dives in a brand new bare velocity 7mm/8mm "semidry" with attached hood, 1 dive in a beat up rental Hollis semidry. Temp hit 49F on almost all dives. Shore temperature was in the 70s. Dives weren't that long as I am new and diving an 80L tank. Went to as deep as 72ft in the new semi dry and about 45ft in the dry suit. Here is the contentious part: I was just as warm or warmer in my new semi dry than the dry suit. I don't have a ton of experience yet, a 400 undergarment would likely make a big difference and my opinions may change, but right now I'm loving the semi-dry. Out of the water, having a dry suit is definitely better. In the water, I really feel great in the semidry. I'm not doing huge underwater times, I'm not diving more than three dives in a day (not more than two so far), I have no idea how serious I'm going to get about going deep, long, or often in cold waters. For now, the semi dry is working great and at $320 on sale, I feel like it was a GREAT choice compared to $2500 for a dry suit. As an FYI you can rent a dry suit for $95/week from diver Dans in Santa Clara after you take your dry suit cert course. I took my cert course through them as a means to refresh and get cold water dive experience and liked it. I'll definitely dive dry again but for my purposes, owning a semi dry for regular use on random weekends in Monterey and renting a dry suit if I happen to do a trip I think warrants it is the right compromise...Also keep in mind that the semidry will wear out MUCH faster than a dry suit. The rental suit I used once was destroyed and nowhere near as warm as my new one. If I knew I was going to dive cold waters most weekends for the next couple years I would not hesitate to buy dry. I know that I could possibly go 6-8 months without diving once ski season is upon us..."