I used a disposable pad to trace a template. BTW, the best disposable pads out there are Always Infinity pads, they can soak up a gallon of windex and still feel dry.
Here's my pattern. You might want to make your pattern longer or shorter depending on your own preferences.
I cut the top layer from some suede cloth (it's supposed to be really good for wicking away moisture), the bottom layer is printed flannel, and there are 2 more layers of plain flannel for the center of the pad.
Sandwich your fabric with the suede cloth (top fabric) right side up, then add the flannel (bottom later) wrong side up, then add the 2 middle layers on top of the flannel. Sew all around the edge, leaving a 2" gap. Turn the pad right sides out and topstitch along the edge closing up the 2" gap.
I added another row of stitching around the center of the pad. Add your snap.
Here's the pad folded up. You can also just layer the fabric together as follows; flannel wrong side up, 2 middle layers, suede right side up. Then stitch around the edge, zigzag over the edge, add an inner row of stitching and add your snap. It's faster but gives you a less finished looking edge.