Layers and effects in Substance Painter have access to many blending modes. A blending mode allow to mix the result of a layer with the other layers at the bottom of it.
Substance Painter perform all its blending modes in Linear space. Note that all the blending modes are not suited for all use case. For example the Normal map blending mode are only useful for the normal channel in a texture set.
You can change the blending mode of each channel of a layer. To switch between the channels use the top-left dropdown available in the layer stack window.
List of blending modes
The following blending are demonstrated with two images (left image being the top layer, right image the bottom layer) :
The normal blending mode the use the alpha from the layer above to composite it (in copy mode) to the layer below.
The passthrough blending mode read the layers below in order to apply its blending. This is mostly useful for filters or for using other blending mode inside folders.
The disable blending mode discard the blending of the layer, displaying only the previous layers.
Replace simply replace the content before. This is useful for example if you don't want to blend your height information with the layers below.
Linear dodge (Add)
Normal blending modes
For more information regarding the normal map blending mode, see the dedicated page regarding this channel : Normal Map Painting