Insulated Thick Sweatshirts is very very important if you live in a cold region because we do not want you to get sick. But at the same time, insulation can make you look baggy.
The basic trick here is to buy a sweatshirt that is lose. Maybe one size bigger will do the trick. The plan here is that when the sweatshirt is perfectly fitted or even tight, it gets all ballooned up and that is what makes you look fat.
A lose sweatshirt will cause disorientation and make you appear slim plus it is also more comfortable. Also using more body warmers and a competitively slimmer sweatshirt will help you. Anyway sweatshirts are for show and only for regions that are not too cold.So you can chose one with less insulation.