This reptile substrate barrier keeps your bioactive terrarium healthy by separating ABG and other mixes from the drainage layer, preventing clogs, excess water buildup, and stagnant conditions. The breathable mesh maintains proper airflow and humidity while blocking loose soil and debris. Made from lightweight, durable material, it's friendly for reptiles, amphibians, and invertebrates. Includes three 18.1" x 18.1" terrarium substrate barriers, easy to cut and fit versatile setups.