Both, Sandstone and Duck materials, are made of 12-ounce cotton and both materials will keep you comfortable and protected during work or every day wear. So what exactly is the difference?
The Sandstone Duck is pre-washed with detergent and softeners, leaving the material much softer with a “broken-in” feeling.. Because it is pre-washed, it is not the best option if you need to repel water / rain.
The Firm Duck is treated specifically to provide a water repellent (not water-proof) outer shell. With this treating process, you are left with a much more rigid and stiff feeling material that will break in over time. This material will need to be treated again if you would like it to maintain it’s water repellant property.
Those are the key main functionality differences, but there are also visual differences as well. The sandstone usually comes out a little browner while the Firm tends to have more of a yellow tint to it. See the graphic below for a representation of the two materials next to each other.