21. Installation – insulating/backfilling the liner. If you plan to insulate you need to decide what insulating material you are going to use. XXFor most purposes, the simplest is vermiculite (brand name "Micafil" – available from any builders' merchant.) This is poured into the void straight from the bag as a loose fill, and allowed to settle around the liner. A vermiculite backfill insulates the liner effectively and also provides useful support when the liner is being cleaned. (Without backfill, the liner can 'flap about' when the brush is being worked, and may get damaged.) XXIf you are installing a liner into an old cavernous chimney you will run into difficulties over the sheer volume of filler material you need. In this case a more economical alternative may be to lag the liner with a 'bandage' of rockwool, secured with stainless-steel or galvanised wire. NOTE;- Use only rockwool as a lagging material, NOT fibreglass loft insulation which can melt at high temperatures. When using the lagging technique take care not to overstress the top of the liner by hanging an excessive weight from the clamps and plate at the top - some extra support may be needed.