sheet of plastic/aluminium (Salford 6 M6 8)

Hiya, does anyone have a big slippy sheet of plastic or aluminium or similar low friction material I could use to reinforce this ‘sled’ I use to tow with my car to move big hay bales that’s on last legs and needs another base? A old plastic sign, car bonnet or road sign for example would do the trick. Determined to not have to buy more plastic when so much must end up in land fill.