If you store your hiking boots and they get moldy like the boot on the left, there are products that can help. The boot on the right was cleaned with Nikwax Cleaning Gel, then treated with Nikwax Waterproofing for Leather with a brown dye in it to put some of the color back in it. Just for good measure it was conditioned and waterproofed with Aquaseal. Almost good as new.
If you find your waterproof, breathable shell is no longer shedding water there are a couple of possible solutions. 1) Run a warm iron over your shell to reactivate the water-repellant finish; 2) If that doesn’t work, you can treat it with a durable water repellent (dwr) finish like Nikwax. Hint: Keeping your shell clean will help it last longer. Wash it with a washing agent that is designed for waterproof, breathable garments like Nikwax Tech Wash.