Casual shirts is best characterised by its collar and fabric. Unlike a Formal Shirt, the casual shirt often has a softer collar, which is made in a button down, or hidden button down, closure. The fabric of a casual shirt is often less formal in its characteristics, being rougher in texture and bolder in terms of pattern and colour. A few examples of casual shirt fabrics are oxford cotton, linen and flannel.
Casual shirts are often best used for less formal occasions such as weekend getaways or a walk in the park. But they can also work as a way of dressing down tailoring. For example, by splitting up your navy suit and wear the jacket with a pair of chinos and an oxford shirt.