# Adjust Surface Emissivity Direction

Surface emissivity is a material property that affects how much heat it radiates. It’s expressed as a ratio compared to a perfect blackbody at the same temperature. 

Emissivity values are set at the material level, whether it's from a manufacturer or a standard material type, so you won’t be able to manually change them. However, many products have different emissivity values on each side. That’s where material direction comes in.

## Adjust Surface Emissivity Direction

To check or change the facing direction of a material with low surface emissivity (less than 0.9), hover over the material in the wall system. These are usually insulation layers or reflective building membranes.

Click the material icon in the top-left corner, and a dropdown will appear. You’ll see the current facing direction, choose 'To External' or 'To Internal' to switch it.

<figure><img src="/files/FKTmGU9CrHWCTOtvDV1g" alt=""><figcaption></figcaption></figure>

As shown in the example above using a Class 1 Single-sided Reflective Vapour Barrier, the R-value can change depending on which way the material is facing, especially in unventilated or slightly ventilated cavities.


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