After supplier quotes for the 1,000 ornamental balusters in a planned luxury home’s porch railings (1) came in at $150 apiece, BOJ Construction of Boston decided to look elsewhere — namely in-house. With the help of outside mentoring and some hands-on training in how to work with molded high-density polyurethane foam, the company’s craftsmen launched their own production.

From a casting of a lathe-turned baluster prototype (2) they created a two-part silicone mold. The mold is filled with liquid urethane (3), closed, and set in a sturdy LVL press (4). The press resists the considerable pressure exerted as the closed-cell foam expands inside the mold; with nowhere to expand to, the foam cures at a density close to...

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