These are the official instructions from Gore-Tex themselves (Jan 2014) which vary a little bit from those issued by the re-waterproofing specialists like Nikwax.
1) So, first step, always read the care label on your Gore-Tex garment. If any of the instructions go against what is below, then bow to the superior knowledge of the garment manufacturer. It could be that one of the fabrics, trims or seals needs a special kind of treatment to keep it working.
2) Next, do up all the zippers, pockets and Velcro cuffs on your Gore-Tex garment so that there are no loose bits to catch on the inside of the washing-machine drum, and the whole thing gets a bit of a more gentle ride.
3) Clean all that gunge which collects in your wachine-machine soap drawer off. Residue from powder detergents and fabric softeners will block the tiny pores in a Gore-Tex membrane. In fact, if your washing machine is old and full of gunge you might want to put a wash through using liquid soap, rather than powdered detergent, before you wash your Gore gear.
4) Set your washing machine to as close as possible to the following settings:
On my washing machine that equates to a 40C Wool wash with an extra rinse cycle and 600 spin.
5) Add a capful of liquid soap. This can be simple soap, or a branded soap cleaner like Nikwax’s Tech Wash.
6) When it’s done, let it drip-dry.
7) Most Gore-Tex garments are also coated with something called a Durable Water Repellent (DWR), which is sprayed on by the manufacturer and is what causes the rain to bead-up and run off, rather than soak in. You will need to either re-activate this using heat, or reapply it if it has worn out on an older garment… so;
8a) If your garment has a DWR applied already – either pop it in a warm tumble-dryer or iron it on a low setting through a towel. Don’t iron it directly because you risk damaging the sealing tapes and the Gore-Tex membrane itself. You don’t need to get the garment ‘hot’, just warm.
8b) If the garment needs a new coating of DWR, then get some Nikwak TX Direct, Grangers Waterproofer or other DWR treatment from your local outdoor retailer and follow the instructions on the pack. For a Gore-Tex garment which is not worn against the skin, Nikwax suggest that you should use a wash-in DWR rather than a spray-on version. There’s more on that in our re-waterproofing guide, here.
9) That’s it, you’re done. Enjoy your revitalised Gore-Tex gear.