Are you planning on using them alone? If so and they are the washable, reuseable type, they should be fine. If they are the disposable kind, the material might not be sturdy enough to stand up the the activity they will probably see.
There is a high risk of pigs chewing them if they are used alone. I advise against this. Eating them can cause blockage in the intestines. If you want to use disposable puppy pads then throw a fleece blanket or something over top of them so the pigs cannot get to them to chew them up.
Thanks. We decided on buying a weather proof tarp and putting sheets over it! I let the males have floor time for the first time 2 nights ago and they loved it. They ran around and seemed like they really enjoyed all of the room in their play pen. It is double their cage size! I'm putting the girls in tomorrow.
I would also not use them alone. It can be very bad for piggies and can make them sick if they eat it. Please don't use them alone. I would put a towel over them and see how that goes. Don't worry so much if they eat the towel though.