We want to determine the infrared spectrum of the diffuse ISM
 with LWS, PHT, and SWS by observing a sample of cirrus clouds
 heated by nearby main sequence B-stars. These observations offer
 the unique opportunity to obtain grating spectra of cirrus over
 the whole ISO wavelength range (2.5-200 micron). Our selection of
 B type stars is based on the Bright Star Catalog and include
 different spectral types ranging from B0 to B9.5. This study has
 several advantages when compared to observations of quiescent
 diffuse clouds. Firstly, model parameters such as distance, radiation
 field, UV and optical extinction are accurately known from previous
 observations. Secondly, the interstellar radiation field has
 a spectrum similar to that of a B5 star, consequently by observing
 different spectral types we can study variations in both the strength
 as well as hardness of the UV field in comparison with ISRF
 conditions. Thirdly, and most importantly, we can provide a
 spectroscopic signature of dust in the diffuse ISM. In addition,
 the spectra will also yield the strengths of the important
 cooling lines, providing a description of the heating and cooling
 of the gas in our targets.