From their website:
The Realm of Battle Zone Mortalis Set contains all four of the Zone Mortalis individual tiles, allowing for a huge range of possible corridor arrangements covering a total area of 2' x 2' (600mm x 600mm). Alpha Complex, Beta Complex, Delta Complex and Gamma Complex are each 1' x 1' (300mm x 300mm) tiles that are fully compatible and interchangeable with each other. These detailed hollow resin tiles, designed by Blake Spence, are perfect for playing games using the Zone Mortalis Warhammer 40,000 Expansion rules, which are available to download here.
The Zone Mortalis tiles use hollow resin, which allows us to produce highly detailed, light and very durable scenery pieces. Due to the casting process of this material, it is sometimes possible to find small air bubbles on these terrain pieces. These are easy to fill as our Working with Resin guide explains. Blast doors shown in some images will be available soon. Figures shown in some images for illustration purposes only. The last image shown to illustrate how expandable the set is.