The rain cover - rain protection for backpacks
Most backpacks are designed to offer good protection from the rain. For strong and persistent rain, it is recommended to use an extra rain cover. Even if the rucksack seams and the zips are sealed, moisture can penetrate the interior after some time without an extra rain cover.
Some backpacks have an integrated rain cover, which is often in an extra bottom compartment and can be pulled out when needed. A bungee cord goes all around the edge, so it can be pulled securely over the rucksack, covering all the pockets, openings and zips.
Rain cover for mountaineering backpacks and cycle bags
Depending on the size of the rucksack or bag, special rain covers are available, which are fixed with bungee cords, hook and loop fasteners or buttons. The material is robust and waterproof, so it protects from mud and dirt as well as rain. So rain covers are very practical for travel backpacks and mountaineering backpacks.
With ultralight rain covers, valuable electronics like camera gear is protected from moisture, and clothes and sleeping bags stay dry even after a long shower. For better visibility in the rain, many companies like Vaude, Thule and Osprey use bright colours for their rain covers. It's available in almost every colour. Also in black, blue, grey and silver.
Correct size for backpack covers
In order for the cover to fit optimally it should also fit perfectly to the backpack size. For daypacks, there are small backpack covers for 20-30 litres and large covers can fit walking backpacks up to 80 litres.
Caution is advised when sharp objects such as trekking poles or ice axes are attached to the rucksack. The rain cover should not be stretched over sharp points or edges, so that it does not tear on the trip but keeps out water reliably.