Neoprene is comprised of many small bubbles. This trapped air is the insulating factor. When trying on a suit, sit in a kayak to make sure you will be comfortable around the waist and can reach forward. Ankle zippers are an excellent feature for ease in taking the suit on and off. Center front zips are great for guys to pee.
Women have the disadvantage of having to take off all the top layers to pee.
Make sure all zippers use plastic slides. Metal slides corrode in saltwater. Velcro entry is used but can be awkward if not in combination with a zipper. Watch out for catching the velcro on your hair or fleece. Neoprene jackets can be too restrictive for most paddlers.