  For the development of charged particle detectors based on straw tubes
operating in vacuum, a special measurement technique is required for the
evaluation of their mechanical properties. A summary of the known equations
that govern straw behavior under internal pressure is provided, and a new
experimental method of a strained pressurized straw tube study is presented in
this paper. The Poisson's ratio of the straw wall, which defines the stability
conditions of a built-in tube, is measured for the NA62 spectrometer straw, and
its minimum pre-tension is estimated.
