Mystery item (Bramhall SK7)

This was found in the back of my late husband’s car and we have no idea what it is. Google reverse image tells me it’s a cover for a backpack but it seems too big for that. It measures 50” (127 cm) long and is about 25” (65cm) wide. It has an elasticated drawstring around the top part and there are elasticated slits down each side. It is made by a company called Cosmos and is 100% nylon. If you can use it, you are welcome to have it.
Dairy ground Estate, Bramhall.