FJ, for that particular style (which is based on unpadded, wrap style straps), I used duckcloth (two layers for the straps, three for the body), or you could use canvas, denim or any decorator weight fabric.

For other styles it is more common to use canvas, twill or cotton drill or denim for the straps and body, with polar fleece for strap padding and quilter's cotton for the front panel.