Given different conductivity values, sigma1, sigma2, etc. Given the thicknesses are the same. Given the layers are in intimate contact with each other. (No air gaps.) Is the whole conductivity for the stackup of layers follow this: 1/sigmatotal = 1/sigma1 + 1/sigma2 + ... ? Is this correct? Is this the same equation as resistors in parallel, capacitors in series, conductors in thermo? I don't know (more like I can't remember - E&M and thermo years ago) and would appreciate the help. Thank you.