Our extra heavyweight T-shirt series is made of two #10 yarns twisted together. We use a yarn called "open-ended yarn" or "air-spun yarn," which is twisted and spun using only the power of air. This spinning method makes it possible to spin only thick staple fibers, which is usually very difficult, resulting in yarns with a slubby texture and containing the perfect amount of air, giving the fabric a rare dry texture. The #10 yarn, which is already very thick for jerseys, is further refined into a double yarn (equivalent to #5 yarn) and this jersey fabric is woven with threads that are actually strong enough to make heavy denim with. The resulting fabric is rough and extremely durable. Also, unlike usual sweat fabric, there is no pile on the back so it can be worn for a longer portion of the year.