I love swimming, I get Childrens Rashvests heat as it is designed to be worn under the suit. For additional heat retention rashvest heat is desirable, polar fleece has more thermal properties that can keep warm. Kids Thermal Rashvests are designed to be rash to be used in a suit or a protective factor. When worn under a collar around his neck and a soft flexible wetsuit rashvests we are a very effective protection against abrasion.