Thick Styrofoam foam board can be found in many building applications to help insulate homes as efficiently as possible. This type of Styrofoam is very dense, about 1.8 to 2.5 lbs. per cubic foot, giving it significant durability. These foam boards can be 2 to 4 inches thick and require special cutting methods with conventional construction tools.
Reciprocating Saw
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Cutting thick Styrofoam is easy with a reciprocating saw. A long blade of the saw cuts through the foam easily, letting you contour curves and sharp angles with ease. Transfer any measurements or designs that you want onto the foam board with a pencil. Cut on the lines with the reciprocating saw and discard the wasted portions. The results are best when using a fine-toothed blade that is typical for metal-cutting applications.
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Box Saw Cutting and Shaving
A box saw consists of a blade with a double-serrated edge. This is a particularly handy tool for trimming the edges of foam on the corners of a building so that the edges of the boards line up. This allows the edge to be sealed properly. The double-serrated edge is also good for sawing upward. To sculpt an edge more, or round it off, take the box saw and rub the edge back and forth along the edge of the Styrofoam. This takes small amounts of foam off the edge like a sander does to wood. Work the saw back and forth and up and down to create a gentle curve, or keep the box saw at an angle to create a chamfered edge detail.
Hot Wire Cutter
Thick Styrofoam board can be cut with a hot wire system. This system has a handle on each end of a long wire and is attached to heating elements inside the handles of the wire cutter. Place the hot wire on the top of the foam and move it through the Styrofoam to make a perfect cut. Holes can even be cut using steel templates. This is typically used in the manufacturing setting, but can be used in the field as well.