I use two pairs: a cheap 2mm Cabela stocking foot with cheap canvas boots. Using a neoprene oversock keeps out most of the sand. 2nd pair is Red Ball boot foots- not as comfy for walking but quick to put on out of the car at 3AM. Unless you fish alot in COLD weather I'd steer claer of 4mm and even 3mm-you'll cook from the inside out when walking the beach. My next pair will probably be one of the breathable boot foots.