Right..whatever you do, dont just re-proof it...you need to prepare the material first or you can "kill it" for good or have a fabric that no longer breaths. Washing will prolong the life of the material and allow the re-proofing to penetrate properly.
First, Goretex etc needs to be washed before re-proofing but DONT use normal washing powder, this will delaminate or block up the membrane.
You need something like Nikwax Tech Wash. Stick your jaket in the washing mashine and add this stuff as recommended. One washed (you will be amazed at the colout of the water, even if your jacket looked clean before it went in
)
Next, you need a wash in re-proofer, and again, totally recommend Nikwax TX Direct wash in proofer.
Once done, let dry and that it for another year or two.
If you use a spray on re-proofer such a Nyloproof on a goretex jacket you can ruin it unfortuantly. Always make sure you use something designed for Goretex
Having said all that, some breathables become waterproof again with a quick iron with the iron set on warm.
