Yes, underlay can contribute to how well a carpet keeps its appearance because it supports the carpet as people walk across it and helps absorb repeated impact. Airstep's published performance material says its testing found that carpet used with its underlay showed improved life and reduced loss of pile height. The effect will still depend on the carpet construction, traffic level, underlay density and resilience, installation quality and maintenance. For a busy room, stairs or hallway, the better question is not simply whether the underlay feels soft, but whether it provides the right support for that particular carpet and level of use.
