PTFE is an excellent diffuser material for instruments exposed to the elements: It has a low coefficient of thermal expansion (0.000122mm per degree Celcius) It has a low moisture absorption (< 0.01%) It is stable against damage by UV radiation The following graph shows the measured temperature-sensitivity of teflon for the temperature range 19 degrees Celcius and 45 degrees Celcius.
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Info, questions and remarks, contact: Richard McKenzie.