Fills with different dampening materials to your liking The columns of the HS series are made of strong and durable stainless steel, which provides good performance out of the box. If you are looking to improve the performance of your audio rack even further, you can use different filling dampening materials to fill the columns, e.g., sand, copper ball, iron powder, based on your preference. This gives you the flexibility to fine-tune your rack to get the best possible sound for your system.