In geometry, an -gonal bifrustum is a polyhedron composed of three parallel planes of -gons, with the middle plane largest and usually the top and bottom congruent.
It can be constructed as two congruent frusta combined across a plane of symmetry, and also as a bipyramid with the two polar vertices truncated.
They are duals to the family of elongated bipyramids.
For a regular -gonal bifrustum with the equatorial polygon sides , bases sides and semi-height (half the distance between the planes of bases) , the lateral surface area , total area and volume are:
The volume V is twice the volume of a frustum.
Three bifrusta are duals to three Johnson solids, . In general, an -gonal bifrustum has trapezoids, 2 -gons, and is dual to the elongated dipyramids.