Air-core uses steel or tungsten blades to bore a hole into unconsolidated ground. The drill cuttings are removed by the injection of compressed air into the hole. This method of drilling is used to drill the weathered regolith (loose, heterogeneous material covering solid rock) as the drill rig and steel or tungsten blades cannot penetrate fresh rock. Where possible, air-core drilling is preferred over RAB drilling as it provides a more representative sample. Air-core drilling is relatively inexpensive and is often used in first pass exploration drill programs. Air-core drilling is limited to depths of 50-60 metres and is drilled using a smaller rig known as an Air-core rig. It is possible to use hammer or tri-cone roller for drilling through cap rock at the top of the hole, but not for hammer tails.