INSULATING BETWEEN UNFINISHED RAFTERS

QUESTION FROM THE STEWART OF AMITYVILLE, NY:

I am looking for a product in to install in between the rafters of an exposed ceiling to keep an unfinished look. i thought some kind of hard styrafoam with a beadboard or sheathing skin would work ? do they make such a product and how would i install it ? just to clarify i would be installing from the inside. thanks for any help.

ANSWER FROM THE INSULATION DOCTOR:

 I have no knowledge of a product in the styrofoam family you could use because of the problem of the fire combustibility.  All styrofoam products require covering due to the fact that they burn vertically and omit a toxic gas.
 
It is important for any product to be covered so that it is not combustible and meets the fire code. 
 
There are products manufactured with an FSK-25 rating which meet the fire code, however, they would not appear to be an unfinished surface.  They normally would have a foil-backed finish or a white vinyl and would not require a drywall covering.  This product can tend to be very expensive.
 
Bruce Jones
The Insulation Doctor