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===================================================================== ==> This proposal requests an upgrade from Priority 3 for UHERBSTM.LHBCL2 ===================================================================== Previous analyses of ROSAT soft X-ray and 21cm HI line data revealed the existence of cirrus clouds located within hot million degree plasma regions. These clouds do not show significant molecular line emissionand densities in the range of tens to one hundred atoms per cubic centimeter. It is surprising that these clouds, more diffuse than the dense globules found in warm HII regions or even in SNRs, can survive in such a hostile surrounding. In our attempt to study these clouds we proposed successfully the observation of two of these clouds, G88+36-2 and IVC 86+38-44, with ISO. We confine our follow-up proposal to G88+36-2, a very local filament, which is located in the Local Hot Bubble. The "Local Hot Bubble" is an irregularly shaped low-density cavity in the ISM surrounding the sun. It is filled with a million degree hot plasma emitting soft X-rays. The filament interspersed with this plamsa shows, however, has low kinetic temperatures, high space densities and is seen to cast a deep shadow in the ROSAT C-Band soft X-ray observations. First observations with ISOPHOT in the mid-infrared showed that emission in the PAH line at 7.7 micron is significantly more confined on the filaments' core than the dust continuum emission of the very small grains. As the photoelectric effect on PAH is a major heating process of diffuse gas, the preliminary ISO result indicate that the heating efficiency of the gas is much reduced, i.e. the gas stays cold. We propose further observations of the cloud as it is necessary - to confirm the result by obtaining an additional scan across the cloud, - and to examine the behaviour of the other dust components in more detail. The philosophy of the FIR observations is similar to the Serendipity Survey Scans, which are able to reveal the variations of the dust temperature and composition (Bogun et al. A&A ISO issue, in press 1996).