You don’t want to overheat in a thick wetsuit in tropical waters, and you also don’t want to freeze or risk hypothermia in a thin wetsuit in chilly temperatures.
This is highly individual. When I’m wearing a full 5mm suit, my buddy only goes for a 3mm shorty.
Also, I will use my dry suit for dives up to 20°C+, simply because of the convenience of being dry after the dive.
Came to say the same, my last dive was 64f/18ishC in a 5mm wetsuit with hood and reef gloves and I was toasty and warm the whole time. My 9 year old snorkeled about for about a half hour in a 3mm suit in the same water without getting cold.
It’s not always down to body composition either, which I’ve seen before. I definitely wear my love of cake on the outside, while my daughter is a fit and healthy weight for her age and height.
Meanwhile I would have been cold in a 7mm in those same conditions. When I was in Cozumel with my local club, most of the people were comfortable in either rashguards or shorties, but I started getting cold in my full-body 3mm by the end of each day.
It’s the air temperature that usually determines whether or not I wear my drysuit. I can wear thin thermal underwear and dive out in 85-degree water just fine, and thicker stuff in colder water.
What I can’t do is put the damn thing on in 110 degree summer heat. By the the I’m in the suit, I’m sweating so much there’s nothing dry about it.
