how important is carpet underlay, will a few millimetres make a difference?

Answer 1

Any carpet layer will tell you that your pad is more important than your carpet choice. Whether you choose a more expensive or less expensive carpet your pad will make the carpet feel better and last longer. Always make sure you choose the most expensive pad. We have built many homes and regardless of the carpet choices in different rooms we have always chosen the top of the line pads. The installers have always told us it's the wisest choice. And in the end result we can tell the difference. In our latest home we chose a lesser carpet for guest rooms that will rarely get used but the top end pad. The difference is remarkable. In the rooms where we chose a higher end carpet, it is fabulous. Pay for the upper end pad. You can't go wrong.

Answer 2

its not important much. its ok if you want more support and prevention from the carpet slipping.