Australian building regulations control the fire properties of cellular plastics used in buildings by setting criteria based on three test methods - AS 1530 Part 1, known as 'The Combustibility Test'; AS 1530 Part 3, known as 'The Early Fire Hazard Test'; and AS 1530 Part 4, known as 'The Fire-Resistance Test'. However, the regulations allow cellular plastics of otherwise unsatisfactory fire performance to be used if they are sealed inside a sandwich panel which meets certain fire performance criteria. These criteria are related to performance in the AS 1530.3 test, and in a 10-minute furnace test modelled on AS 1530.4. This paper summarises the regulatory situation and discusses a series of tests in which a limited range of lightweight sandwich panels were subjected to a 10-minute furnace test. It was found that none of the lightweight sandwich panel systems assessed performed well in the furnace test. In addition, difficulties were experienced with the test procedure and interpretation of results.