Fusion PCB Specification -- Provide separation dimensions between layers.
For computing strip-line impedance it is important to know the distance between conducting layers and the dielectric constant of the insulator material. If averages are provided please also provide variance
Anton S. commented
This is board stackup. Please vote here http://support.seeedstudio.com/forums/243707-my-seeed-idea/suggestions/9357699-stackup-information-pcbs