This is a simple ribbed cap that can be knit fairly quickly.
The original used size 7 (4.5mm) needles and less than a skein of worsted weight yarn. A knitter could go up a needle size or two for a less dense fabric or to adjust the fit for larger head sizes. Or the knitter can add multiples of 8 stitches, adjusting the number of decreases accordingly. Either section of the ribbing can be lengthened for a custom fit. The pictured caps are slightly under 9 inches overall.