We have a monster size litter tray which our three cats share and using litter tray liners has been an absolute boon in dealing with an unpleasant job in a civilised manner. We have been using Ferplast liners which are excellent - the only drawback is the excessive price.
We have tried several alternatives without finding anything comparable - too small, or just a single sheet of plastic not shaped being the main issues. However, these are great and are just as good as the Ferplast ones. They are thick enough not to tear when the cats dig and are shaped to the litter tray. Large enough for the largest litter tray I would think, certainly plenty big enough for ours. Best of all they are a huge saving on the others we have been using. Definitely a Five Star product and highly recommended!