Advance Ultra Core combines limestone and PVC into a stable composite that can stand up to humidity, moisture, and mildew, wet, hold, or cold, it will hold shape and size. Big Ass Planks Advance Ultra Core has passed CE standards for fire resistance, which means it won’t spontaneously combust and if it combusts, the fire puts itself out in five seconds. Does not contain benzene, formaldehyde, or heavy metals. It is abrasion-proof and slip-resistant and the core is rigid, making for easy and precise installation.