This cotton button-up is the kind of clean style and soft, stretchy comfort that goes from trail to everyday life with ease. Crafted from a soft cotton blend with a hint of give, it features a regular fit, button-down collar, and a handy chest pocket. Columbia offers this long sleeve shirt in multiple colors and sizes. Extended sizing available. Regular Fit. To ensure the size you choose is right, utilize our sizing chart and the following measurement instructions: To determine the neck size, measure at the base or thickest part of your neck. For the sleeves, start at the center back of your neck and measure across the shoulder and down to the sleeve. If you come up with a partial number, round up to the next even number. For the chest, measure at the fullest part of the chest, under the armpits, and over the shoulder blades, keeping the tape measure firm and level.