The makers of your footwear have taken a lot of care in ensuring that the Gore-Tex membrane within is well protected and looked after. Over time however you may notice that perhaps the breathability can start to become less effective. This is due to a build-up of dirt and oils from the outside world as well as your feet working hard within. To counter this, simply make sure that both the inside and outside of the shoe or boot are kept clean.
Leather footwear will protect the lining from dirt coming from outside, however, when cleaning the inside, or the outside of a lightweight synthetic shoe or boot, we recommend an occasional, good clean with Nikwax Tech Wash.
To clean the inside, remove the insole and mix water with a little tech wash. Using a sponge, cloth, or other soft cleaning tool soaked in the Tech Wash solution, scrub around thoroughly within making sure to soak and wipe all the nooks and crannies. Following this be sure to rinse out with more water and allow it to dry naturally at room temperature. Once dry, you can put the insoles back in (feel free to give these a clean as well with the same solution.)
You can also use this process on the outside of a synthetic Gore-lined shoe or boot.