Outwell Reel Airbed Double - https://www.outwell.com/en-gb/ecommerce/sleeping/reel-airbed-double.
I overinflated it, so some of the internal ribs detached, which means it is no longer flat - there are 'lumps' where two ribs belnded into one create a high point in the mattress.
Fine as an air mattress if you're not too fussy, or the material could be used to make or patch something else. Worst case scenario, it's a hardwearing thick material that could be used as a weed membrane.