Review on 🎒 Joy Walker Waterproof Backpack Rain Cover (15-90L) - Upgraded Anti-Slip Straps and Triple Strengthened Layers for Hiking, Camping, and Traveling by Robert Dickinson

I ordered the small size and tried it on my 30 liter bag. The smaller size (calculated for 15-30 liters) fits perfectly. The design is basically like a large shower cap with a rubber band around the hole. It stayed in place for me but partially slipped down when worn. It would have helped, but most likely water got into the main compartment during heavy rain. Exactly where it lands on your pack likely depends on the exact configuration of the straps and stitching. The large size has a strap running down the middle that you can use to tighten it. The extra room allows you to bypass most of the pack and stay in place. It looks like it will keep the rain out. Both come with a storage pouch, which is a nice added value. I plan to buy more but would prefer the larger size for all but the smallest packs (20 liters or less).