The Back on Track Long Johns are now also available in a 100% polypropylene fabric. The polypropylene fabric's unique advantage is that it is both extra durable and very effective at wicking away sweat and humidity. It also is much less likely to get burled than polyester as the polypropylene fabric has much longer fibres. However, polypropylene is less elastic than polyester, so one needs to chose size more carefully. The fabric is smooth and soft. Due to its excellent wicking qualities, this garment is well suited as underwear or an extra layer during physical activity. Comes in a range of sizes (Extra Small, Small, Medium, Large, Extra Large, XX Large and XXX Large).