# I can't find the material I need, what can I do?

There are two options here:

1. If you know the building fabric composition but not the U-value, you can click on the *\[+\] Custom material* button and select *Build Layers*. You can then add each layer of building material from the drop down menu and its associated thickness (mm). The software is then able to calculate the corresponding U-value of the building fabric.
2. If you already know the thickness of the material and its associated U-value then you can input this directly by clicking on *\[+\] Custom material* in the material selection section and clicking *Enter U Value*. This will allow you to type in a custom name, U-value (W/m<sup data-renderer-mark="true">2</sup>) and thickness (mm) for the entire building fabric.

For more information on this topic, see our guide on [Managing Your Material Library](https://help.heatpunk.co.uk/books/plans-task/page/managing-your-material-palettes-and-library).