There are generally two forms of wet room shower tray formers available and featured in the kits below:
Self-supported: Like "nicholls and clarke formers" or "AKW triform linear form" both used for Tile or Vinyl . These trays are stronger and will accept high point loads, like wheelchairs and freestanding chairs.
Support required: EPS (expanded polystyrene trays) like "AKW Duraform" which requires full support underneath and is only usable with tiles. These types of trays can not be used with wheelchairs or similar high point load items.