This durable Cavity Sleeve by Timloc has been designed to create a steady ventilation between a buildings interior and though to the external walls. One sleeve suits a wall that is 275mm thick. If necessary, two sleeves can be connected together to suit a thicker wall. This can be done by joining the ends together and trimming them. If a wider cavity application is needed, you can use a telescopic extension. This product also must always be used with Timloc’s Airbricks. This cavity sleeve provides a solution to suit a double stacked Airbrick (9" x6"). If you are needing a solution to suit single (9" x 3") Airbrick, we also have Timloc’s 9x3" Through Wall Cavity Sleeve 1 Airbrick in a Box of 20. To prevent any unwanted water from going across the top of the cavity sleeve, it is strongly advised that you should install a segment of Horizonal Cavity Tray above the Airbrick and Cavity Sleeve. This should protect both accessories from the water. Features & Benefits Unrestricted free airflow Lightweight and easy to handle Durable and totally resistant to decay Manufactured to BS EN ISO 9001 and BS EN ISO 14001 Product Specification Maximum Area Per Cavity Sleeve: 12300mm2 Colour: Black Suits: Two Stacked Airbricks