As defined by the arbitrary rules that I have assigned myself that I follow when I build... All ship classes from corvette and up are required to have no less than 2 meters of hull between pressurized cabin and space, therefore ships have an inner and outer hall. All larger military vehicles typically have a layer of shield capacitors between the inner and outer hulls. I suspect as I build bigger ships my layer system may adapt but I probably won't build anything else until future versions with more complete features, such as hyper-drive, the HP system and the Engine Overhaul.