Put the ultra-violet protected thread on the sewing machine and set the machine on a medium length straight stitch.

Put the wrong sides of the waterproof fabric pieces together. This is the opposite of what you would do for a standard seam.

Sew the fabric using a 5/8 inch seam allowance. Do this by sewing 5/8 inch in from the raw edge of the fabric.

Spread the seam open and cut off the raw edge by placing the thin tip of the scissors 1/4 inch away from the seam line on one side. It does not matter which raw edge you cut off but right-handed people will find it easier to do step 5 if they cut off the right edge and left-handed people will find it easier to cut off the left edge.

Wrap the longer side of the seam around the shorter side. Place the raw edge right against the seam line and either iron the fabric down or pin it with the straight pins.

Sew 1/8 inch from the folded edge of the seam. The seam will resemble the seam on jeans when you finish this step. If you are sewing on a heavy waterproof fabric like canvas you are done. If you are sewing a light finely woven fabric go on to step 7.

Sew 1/8 inch from the original seam line. This will give extra durability to the seam on a light fabric.

These basic guidelines will create a tight, leak-proof seam on most waterproof fabrics because flat felled seams should not leak. If extra waterproofing is preferred a stick or tube of waterproofing can be purchased almost anywhere that sells camping equipment or sewing supplies.