RRP £169.99 Listing is for one case of 16 sheets. Damaged packaging. See photos. The JG Underfloor Lowfit Castellated Panel is a 16mm thick plastic panel designed for use with 12mm pipes in a hot water underfloor heating system. It covers an area of 9.6m2 and comes in a sleek black colour. This product from JG Underfloor is specifically designed to provide efficient heating while being discreetly hidden underneath the floor. Perfect for keeping homes warm and comfortable in a stylish and unobtrusive manner.