ACRE roof substrate is made from the porous rock spongilite, crushed expanded clay (Ekogrit), and peat.

Spongilite is a relatively light, porous rock. It possesses a number of valuable properties for roof substrates, enhancing their utility.

• lower specific gravity
• high water absorption (approx. 20%)
• good water permeability
• neutral pH
• weed-free and clean – contains no pathogens or plant pests

The substrate is suitable for undemanding plants such as mosses, sedums, and certain other xerophytic perennials and grasses that can go without watering for extended periods. It is used in layers 4–20 cm thick. It is characterized by high permeability, as it also serves as a drainage layer and must therefore be able to carry all excess water to the drainage system.

The development of the range of roof substrates with spongilite for green roof gardens took place in collaboration with the Silva Tarouca Research Institute for Landscape and Ornamental Horticulture in Průhonice. ACRE roof substrates with spongilite are protected by a Utility Model Registration Certificate issued by the Industrial Property Office of the Czech Republic.