What fabric to use to extend the length of a plastic raincoat?

[THX1138]

I have a raincoat that I wear when I'm cycling in the rain and it almost covers my knees by not quite so they still get soaked. I was thinking I could lengthen the coat by adding some waterproof fabric along the bottom but I'm not sure what is an appropriate fabric to use and label has faded so I can't tell what this fabric is made from except that it includes nylon. I could use a spray adhesive and/or sew along the existing hem. The coat is grey and blue so I'll probably aim for a dark grey but a close match is not important.

[Vegegrow]

Pennine outdoor fabrics do samples http://www.pennineoutdoor.co.uk/fabrics
I've never used them myself but I know others on here have ..

[THX1138]

Thanks. Polyurethane-coated polyester or nylon seem like a good idea!

[Vegegrow]

Can't help with the fabric choice but only thoughts are that stitching will perforate the waterproofness.. ( don't think that's a word is it ?) perhaps you should cover the stitching line with some sort of waterproof tape?