They can stay in your cooker permanently andare a heavy industrial grade non-flap material that will last for many years. Wash them easily in warm soapy water or in the dishwasher. Much easier than attempting to clean the ovens themselves! In Aga 'Total/Dual Control', 'City', 'R' & 'ER' models and Electrikit converted range cookers make sure the liner is placed on top of the oven floor grid.
The liners are one size (530 x 340mm) to fit all ovens of 2, 3 and 4 oven cookers - you'll need to trim them 4cm shorter for the roasting and simmering ovens of 'Deluxe' and 'Standard' models (an easy job with a pair of kitchen scissors).
The 'lip' of aluminium or stainless steel in these ovens should be left visible with the liner covering the steel main section. Cut a small section (50mm deep x 40mm wide) from the rear left corner of your roasting oven liner to leave the vent hole in the floor visible.