I was out for a walk with a friend who was admiring my mat, she hadn't come across them before.
I did the usual thing of packing up and fastening my rucksack while still sitting on it, and explained that this always happened, surely not just to me, miracle I still had it etc etc.
50 yards beyond our lunch place we turned a corner and there on the ground was a posh blue foam sit mat. We hadn't seen anyone all day, so she picked it up.
I have a theory that there is a circulating collection of mats that go round and round the walking community.......and I have contributed my share.