Is it EVA or PVC? I recommend you do a Google Search to see if you can find what it is you need. Love Chris

There is an iron on vinyl product that you could put on at the end before the satin stitch - but there would still be little needle holes where you sewed the last part of the patch (the satin stitch around the edge - at least I assume that with a patch). Other than that you would have to look for some liquid type product you could put on after it is on the jacket.

I think teddy is right, iron on clear vinyl that would be the way to go.

If you have a Joann Fabric near they have a vinyl/laminate that you use to protect fabric. i think it is in with the interfacings,etc. Ask at the store, they will know what your neeed.
Another option is to go to a sporting goods store and get a can of the waterproofing spray that they sell to use on winter boots. You could do your patches then give them 2-3 coats of spray and then sew them on.
This would be the least expensive as a can of spray goes a long, long way.

Before doing any jobs for these people, make sure that you prepare a waiver stating that you are NOT responsible for any loss or damage that may occur during the process of alterations made to the jacket. Demand that it be signed by each individual. You don't want to be "on the hook" for replacing costly jackets.

I think I'd test out a few techinques before stitching on a jacket. Are the jackets waterproof?

thanks for all the answers, i will go to joanes hopefully they can help.and yes i will see about getting them to sign a paper incase a bobo happens, so glad your all here, DORIS