A heavyweight long sleeve t-shirt is built for layering in cooler months and for standing alone when temperatures drop enough that you need real fabric weight without a sweater. The weight of the cotton means the shirt holds its shape through wearing and washing and does not pill or thin out over time. The fabric should have enough body that it does not cling to your body in a way that feels unflattering. The sleeve should have enough weight that it sits properly without twisting. The fit works best when it skims your body without being oversized or tight. These are the heavyweight long sleeve t-shirts that layer beautifully because the weight means they do not create bulk and the quality means they last through repeated wearing.