These covers are made from waterproof materials like ripstop polyester with a PU coating, designed to shed water effectively. They fit snugly over your pack with an elasticated hem and securing straps, leaving your back system and shoulder straps clear so you can carry on without issue. Many come in bright, high-visibility colours, which is a great safety feature if you’re out in misty conditions or on a roadside section. They pack down into a tiny stuff sack, so you can always have one ready at the bottom of your pack. It’s a small bit of kit that can save a lot of misery.