Plastics

The walls of this castle are made with closed-cell extruded polystyrene—Styrofoam.

Just how do you mean that, sir?

In the classic film The Graduate, a business executive tells a young college graduate (played by Dustin Hoffman) that “There’s a great future in plastics.” Little did he know he was talking about how they could be used in theatre sets. In this column I want to focus on a small subset of plastics, namely foam, and their use in theatrical construction.

Plastic foam is a thermoplastic material that has been blown up with a gas. (That is a simple definition but will suffice for this column.) The best-known word used to describe plastic foam is “Styrofoam”—which is a bit of a misnomer. Styrofoam is actually the brand-name for a closed-cell extruded polystyrene material (XPS). The cups you use and call “styrofoam” are actually made from expanded polystyrene (EPS).

The difference between XPS and EPS is the density. EPS is less dense and therefore easier to cut and form in large sculpture projects. This article will focus mainly on XPS. Your design will drive your choice of plastic.

A good use of XPS is in creation of walls, especially ones that are curved. For a production of Once Upon a Mattress my designer wanted to have curved turrets as part of the castle. Our first step was to cut ½-inch plywood into large 4-foot diameter by 23-inch curves. We connected two of these curves with 1-by-3 boards to create the inner wall structure. When first presented with the creation of these walls the students were unsure how to face the inner structure and did not quite believe that I was going to use foam.

Styrofoam is flexible enough to hug a curve, but dense enough to hold a screw.

I went to Lowe’s and picked up ½-inch thick, 4-by-8 sheets of wall insulation made of XPS. (I tend to get funny looks at Lowe’s when I tell them what I am doing.) Still, the foam was pliant enough to accept the curve without breaking and dense enough so that drywall screws held the foam against the curve. For our final touch we mounted a piece around the back halfway up so that we could cut in the crenellations at the top of the wall.

Beatles, Radiohead and Roller Coasters

Along with polystyrene, polyethylene can be expanded into foam products. Polyethylene foam is a closed cell product with regular small cells. Created from low density polyethylene (LDPE), the foam is very light. One common product made of LDPE that anyone with children and a pool will recognize is the pool noodle. The closed cell structure keeps the foam from absorbing the pool water.

I recently used a version of the product in a set for Drop. The set is a roller coaster car, and we were performing the show in our black box theatre so the set was small. I used a curved bench seat mounted on a 4-foot-by-4-foot platform 4 feet off the ground. In order to simulate a roller coaster car I needed a lap bar to hold the actors into the car. I fashioned the lap bar from PVC piping so that it came over the actors’ heads and rested on their laps. This didn’t have a very finished look so we went out and bought pipe insulation.

Pipe insulation is a hollow tube split down one side with glue on the edges. The tube is—you guessed it—made of polyethylene foam. It slipped right over the pipe, and I only needed my Leatherman to make the 45° degree cuts at the corners.