Hoods 75% of your body's heat loss leaves through your head. That's why neoprene hoods are so valuable. They take a bit of getting used to using while scuba diving or snorkeling, but the effort is worth it. You'll be more comfortable for longer periods of time in the water. Scuba and snorkeling hoods are made of neoprene and the most important aspect of fit would be that you don't get one that squeezes your neck too tightly. Tight around the faces is OK, tight around the neck is not. If you can swallow while you are wearing your hood, you're probably fine. Some hoods have no neck, usually called beanies, and although more comfortable, they will not keep you as warm. They're good for surfing and snorkeling, or scuba diving in warmer waters. Drysuit hoods usually have a longer neck than a beanie and are designed to go over the top of your drysuit neck seal. Standard neoprene hoods are designed to go underneath your wetsuit neck seal. There are also neoprene hooded vests which will do a great job of warming your core. They are generally worn on the inside of your wetsuit but some folks will wear them on the outside. Another consideration is the type of neoprene a hood is made from. Standard neoprene is the staple, but many manufacturers make hoods now from stretchy neoprene and that has shown to be a great option and more comfortable for divers who really don't like the feel of a hood.