Foureir Transformed infrared spectroscopy

Why we are using polystyrene film (0.10mm to 0.038mm) only for calibration?
what is the purpose of using only that film on full wavelenth

Polystyrene gives wide range of wave numbers in Mid IR Region. hence it is selective.

the thickness is validated to get good reslution. usually it is 35µ.

Bujji Reddy.