What a smart material is
A Smart Material is an asset created in Substance Painter which can generate textures that take the geometry of the targeted 3D asset into account. Furthermore, if you change the 3D asset, the material will adapt the generated textures.
This can be very useful in the context of a production, as you carry out the work just once, and then reuse it as much as necessary.
It has a .spsm format.
When adding a Smart Material on Substance Share, it will automatically detect the image file embedded in the asset and use it as a thumbnail.
In case it does not detect one, it might be because the Smart Material has not been created recently enough to have the thumbnail embedded in the file.
In that case you can import it in a newer version of Substance Painter and export it from there, the upload will now work properly.
Image: "Lichen" by Collod Liam (link)
How to create a smart material
Creating Smart materials can only be done in Substance Painter, and they can only be used there.
Smart Materials are easy to create!
You can follow this tutorial to learn how to create a peeled paint effect with the use of simple fill layers and anchor points.
You can also find more information on how to create Smart Materials in the documentation here.