Making beautiful, affordable design available to the masses was a central tenet of mid-century modernism–one that never would’ve been possible if not for the advent of a key material: plywood.

That plain little sandwich of lumber and glue–with its origins in ancient Egypt and its reinvention under the auspices of 20th-century military research–gave designers from Alvar Aalto to Charles and Ray Eames the raw material with which to shape some of the most iconic furniture of the past 100 years.

The Eameses called their plywood-molding apparatus the ‘magic box.’

Plywood: Material, Process, Form is an ongoing exhibit at New York MoMA that reveals the huge variety of forms designers managed to wring from this “modest but consummately modern material,” as the show’s text says. What made plywood so special? First, it helps to understand what plywood is exactly. It’s three or more sheets of thin wood that are assembled, their grains at right angles to each other, then laminated with glue. The perpendicular arrangement of the grain makes plywood exceedingly difficult to break. At the same time, a machine can easily bend and shape the material, so it’s optimized for mass production.

Designers exploited these qualities to make practical, economical objects for the home and beyond. Arne Jacobsen designed a lightweight, stackable side chair–nicknamed the Ant Chair for its node-like body and skinny legs–that was originally used in a cafeteria. Charles and Ray Eames molded splints for injured servicemen, among many other products; their studio was the ne plus ultra of plywood experimentation. And Alvar Aalto’s gracefully curling Paimio Chair–which is widely admired for its sculptural shape–was actually developed for patients at a tuberculosis sanatorium in southwest Finland; using plywood, Aalto was able to customize the angle of the back to help sitters breathe more easily.

For all its pragmatic appeal, there was something of the occult in the way people talked about plywood. Take the Eameses, who called their plywood-molding apparatus the “Kazam!” machine or the “magic box.” Or Marcel Breuer who in 1943 proposed a plywood house that would appear to float in midair and would “weigh a third as much, cost only 70% as much and, knocked down for shipment, would occupy only 30% to 40% as much packing space” compared with standard prefab construction, he said. (It was never built.)

That sort of hyperbole might seem silly today, at a time when plywood is used for everything from skateboards to scaffolding. But it was hardly unique. Nowadays, instead of glue and lumber, we’re being sold on the supernatural powers of nanomaterials and carbon fiber. The promise is the same, it’s just the material that has changed.

The irony is that the very design objects that showcased plywood’s greatest potential are beyond the reach of most people today. The Eames’s beloved molded plywood chair checks in at around $800. Aalto’s Paimio chair retails for a whopping $4,000. The humble material that was supposed to serve up affordable, beautiful design is still plenty beautiful. But affordable? Afraid not.