What is the difference between a bike pack that is “water resistant” versus one that is “water proof”? Ride often enough, and you will get caught in the rain. That is just a fact of cycling life. If you are participating in multi-day rides and tours, or regularly bicycle commuting to work, dealing with rain is a certainty. Keeping yourself dry is complete topic by itself. But what about the gear you carry on your bike in rack trunks, panniers and handlebar bags?
Most nylon fabrics used in bicycle packs have an internal coating that is water resistant. This coating that holds a nylon fabric together will also keep items inside dry through the occasional shower However, this water resistance is compromised where the bag is sewn together. Also, the outer fabric layer can still get wet, and gradually soak through the internal coating and sewn seams. So most fabric manufacturers will add a external fabric coating (Scotchguard or similar products) that repels water and also prevents stains. Water will bead up and run off the pack, slowing down the process of soaking through. You can also improve water resistance with design features like flaps over zippers, (or using water resistant zippers) and seam placement.
When there are multiple pockets and zippers on a pack, the only way to completely keep water out is with an accessory rain cover. The rain cover will typically fit around and over the pack like a shower cap, will have as few seams as necessary, and may include a drain at the bottom. Rain covers are usually very light fabrics, and intended to be used only has needed. This will keep the rain cover from loosing both its external and internal coatings (and water resistance) from daily wear and exposure to sunlight.
So by combining a water resistant fabric, good design and and another layer of water proof protection, the end result is a water resistant pack system.
Next, I will talk about water-proof packs
Find a full selection of bicycle packs from Arkel, Bontrager and KoKi bicycle packs at all three Bicycle Garage Indy locations: Bicycle Garage Indy North (Indianapolis, Dean Rd at 82nd St.), South (just west of I-65 on County Line Rd, Greenwood), and the new BGI Downtown, in the Indy Bike Hub YMCA at City Market.