Page 73 - Between light and shade

Light, transparency and reflection

since the 1960s for outdoor tents and also to cover
large enclosed spaces, beginning a new chapter in
the art of building. These flexible surfaces, which
can only have a negative Gaussian curvature 73,
are light (1 to 1.5 kg/m² compared to 20 kg/m² for
8 mm glass), are produced as easily as boat sails
and are easy to work with. They currently have
a permissible strength of 100 to 150 KN/m. Even
though they are white, their light transmission
(LT) is less than 10%.

PTFE 74 coated fibreglass fabric appeared in
the early 1970s 75. It has the same mechanical
properties as modern polyester — PVC fabric,
is a little more transparent, fire-proof, less dirty,
theoretically more sustainable but, stiffer and
more fragile, and is difficult to work with.

Frei Otto (1925-2015) 76 was one of the first
people to realise the benefits of these “flexible

73 At atmospheric pressure, flexible envelopes subject to internal
pressure can themselves adopt all kinds of curves (yet another
different chapter in the art of building).
74 PTFE: Polytetrafluorethylene, discovered by chance by Roy.

75 J. Plunkett (1910-1994) in 1938, at Dupont.
It is the result of a collaborative effort by Dupont, Owens-
Corning, Birdair and Saint-Gobain.
76 Frei Otto (ed.), Tensile Structures, Vol. 1: Pneumatic Structures;
Vol. 2: Cables, Nets and Membranes, Cambridge (MA), The
MIT Press, 1967/1969 (original version in German, 1962/1966).
As an architect (1925-2015), he also studied large tensile shapes
in the form of steel cable nets and used them for the West
Germany Pavilion at the Montreal universal exhibition in 1967
and then for the roof of the stadium and swimming pool for
the Munich Olympic Games of 1972. These costly and complex

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