Where should a subsurface map be plugged into?

[AegonTargaryen]

In the Principled BSDF shader, under the subsurface section, there are multiple inputs. If I have a subsurface map from Substance Painter, where should I plug the map into? Weight?

[julperado]

Weight is the mix between Diffuse and SSS, so I’d suggest to always leave it either at 0 (fully diffuse) or 1 (full SSS), and instead plug the SSS map into the Scale input.

In the screenshot I set Weight to 1 to “activate” SSS full, and connected a checker texture to the Scale, so where the texture is black it equals to 0, meaning the SSS effect is not visible, and where the texture is white it equals to a SSS scale of 1. IMO using the Scale input gives you more control and it looks better.

[Jvry]

According to Brecht over on Devtalk (emphasis mine):

There are multiple valid ways to use the subsurface radius and scale.

One is that you can use the float to set the scale at which you are working, and then treat the RGB values as a color, that you can texture if needed. Another is that you can set the RGB values to absolute distances, and then have a texture map for the float to vary the distance.

Side note: the radius values are vectors that can be used outside the 0-1 range, but are mapped to colour. There was a lot of back and forth on whether the socket should be yellow or purple, but seems like it is staying the way it is for the time being.

I think in practise most people are going to find plugging maps into scale as julperado does above the more intuitive, but test the two methods and see what suits you.