Abstract: A hot press including a displaceable sleeve for surrounding materials of a multi-layer substrate under a reduced pressure condition, a gas pressurizing condition and a heating condition with thermal plates. Upper and lower sealing units seal an interior of the sleeve, with a mechanism lowering and raising the sleeve. A pilot check mechanism prevents a lower bolster from raising/lowering upon the reduced pressure condition and the gas pressure condition, and a retainer maintains the lowered or raised condition of the sleeve. The multi-layer substrate is formed under the reduced pressure condition and the gas pressure condition. Accordingly, the atmosphere and moisture between the materials of the multi-layer substrate and volatile composition are removed. Additionally, a void generated during the heat and pressure process by the heating plates is eliminated from the multi-layer substrate.