There’s nothing worse than having a having a stubborn rain jacket zipper that won’t zip when it starts to rain heavily. To prevent this, I lubricate all of the zippers on my hiking coats, sleeping bags, and shelters at least once a year McNett Aquaseal Zip Tech<. Application is easy. You simply run the lubrication stick up and own both sides of a zipper, close the zipper, run it up and down a few times, and then wipe off any excess lubricant with a paper towel. I first learned about this product for lubricating the zipper on my whitewater kayaking dry suit, which is plastic, like a lot of the zippers on watertight or lightweight backpacking gear.Disclosure: The author owns this product and purchased it using their own funds.