Remember proper nix wax you heated it up and when turned to liquid insert into the leathers bloody good stuff shame they band the stuff but can still get the spray very good stuff
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They recomend that you rub the wax on, then hold the trousers over a stove to melt it in - they don’t say whether you should be wearing them at the time…
I have used the Nikwax in the past for my Goretex stuff. It will prevent water from being soaked at the outside nylon fabric (beading effekt). But you can’t fully prevent the soaking from happening in heavy rain. The membrane is supposed to keep the water out.
Btw. under rain conditions all membranes loose their breath-ability so sweat will accumulate inside.
I have used mild tumble dryer conditions to activate the Nikwax as described.
The Fjällraven wax is for their G1000 cotton material to make it water repellent. Goretex will not like that I guess.
If you are going to put it through the domestic washing machine you will need to do 4 or 5 soapless rinses first. You need to remove traces of biological wasj=hing power and more importantly, fabric conditioner from the machine. My machine has a rinse and spin again option that along with higher water level option, fills with clean cold water and then runs the drum for 5 mins before pumping out and spin. I run this program with nothing inside and once it gets to the spin stage I abort it and restart it. Then I add the stuff to be proofed and the Nikwax proof to the drum, close the draw and do a cold wash with the detergent drawer removed so no traces of detergent etc. get added.