It's thermal.
Hoddies are made of heavyweight cotton. While they can actually capable of adding a fair bit of warmth, cotton soaks up any sweat or moisture, then gets cold and clammy.
Most other sweatshirts on the market today are made of some kind of blend, usually cotton and polyester.
Sherpa fleece is made from polyester and bases made from these are very capable of moisture wicking and can add much warmth while remaining breathable. The downside? They stink.
Sherpa fleece looks like leather on one side and sheep wool on the other, but the entire fabric is synthetic.
Jackets and sweatshirts made from thermal fabrics help you stay warmer in any condition. Thermal fabrics are useful for all kinds of projects where you want to keep hot stuff hot and cold stuff cold.
Because of the metallic coatings common to many of types thermal fabrics, they can withstand high temperatures without scorching.
A thermal jacket made by ThermalTech is capable of harvesting the energy of the sun to keep its wearer warm. The ingenious new fabric is constructed with stainless steel yarn, and it gathers both solar rays and artificial light, resulting in a material that is as lightweight as it is cozy.
In a 4 season climate, it’s nice to know how to dress warmly enough to stay comfortable outdoors. Here 12 Tips to Help You Choose Warm Clothes.