The MS.405 was a low-wing monoplane of mixed construction, with fabric-covered wooden tail, but a bonded metal/wood material ("Plymax") skin fixed to duralumin tubing. Plymax consisted of a thin sheet of duralumin bonded to a thicker sheet of plywood. Morane-Saulnier had a long history of producing warplanes dating back to the pre-First World War years, but in the inter-war period, they had larger concentrated on civil designs. The aircraft was a departure for them, being their first low-wing monoplane, first with an enclosed cockpit, and first design with retracting landing gear. Prior to this, their most modern designs were fixed-gear parasol monoplanes.