# 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 **\[+\] Custom material** then 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).