Wall thickness boundary condition

mskim

Hi. Does anybody know how the wall thickness boundary condition will be applied? I'm doing 3D modeling with very thin material generating heat. In this case, we can have boundary condition with imposing wall thickness. I'm just wondering which direction is for generating finite wall thickness. For example, if I have a surface at x=0 and impose 0.05mm of thickness, does this thin wall will extrude into positive x? If not, negative x or centered? I appreciate your help in advance.