Flex is a system of flexible elements that can be used in many ways, such as wide doorways, stairs or as protection from the fireplace or stove. When you buy a Flex playpen, you can convert it into a Flex XL or M by adding or removing two wall fittings. All Flex grilles have the same extra wide door and can be opened by an adult with one hand. The grilles are easy to install. Everything you need for installation is included in the package.