The trim handles the lap joints and locks the boards in place to prevent separation on uneven ground. The trim pack is made up of pre-drilled 3-one/four inch wide major rails and corner moldings that attach into the raised mattress with bundled screws. The mattress arrived with a fiber-mulch liner https://raised-wooden-garden-beds66542.blogzet.com/indicators-on-raised-wood-garden-beds-you-should-know-41945403