The first step in designing a fabric structure is to create a
form with sufficient pre-stress, or tension, to prevent it from
fluttering like a flag or sail. Lightweight structures with
minimal surfaces optimally should have double curvature — a
surface that possesses a high-point (positive) curvature along
one principal axis and a low-point (negative) curvature along
the other principal axis. Anticlastic surface forms have double
curvature in diametrically opposite directions, like a saddle,
while synclastic surface forms have double curvature in the same
direction, like a balloon. The degree of curvature depends upon
the type and weave of the fabric as well as the type and
direction of the loads. The three basic forms associated with
tensioned fabric structures are the hypar (hyperbolic
paraboloid), the cone, and the barrel vault. The hypar, or
simple saddle, is often a square or rectangular form in plan
that in elevation is a series of high and low points. Mast- and
point-supported structures are cone form