A one-piece blank of thin semi-rigid material, such as cardboard, formed into a series of rectangular panels hingedly connected at parallel foldlines and two trapezoidal pairs of interlocking flaps, may be easily assembled to form a foldable binocular. One panel contains a pair of objective lenses and another panel contains a pair of ocular lenses. When folded, the objective lenses, and optionally the ocular lenses, are protected from scratches and smudges by a pair of rectangular flaps formed by glueing certain panels together before assembly.