When we first got the cage liners, they were so soft and cuddly looking, it looked like you could just go to sleep on them. But as soon as the pigs would lay a couple poops on them, they stood out way more than on bedding. The only solution was to sweep up the stuff every single night. At least it's easy to sweep with a little broom and dustpan.
It did serve to highlight that the pigs can produce their own volume in poop in about three days.