I have been using Wet & Shape craft cloth for about 15 years as a layer over corrugated (before two layers of Hydrocal) to form the shell of my mountains on my HO scale Oil Creek Rail Road.
Wet and Shape is a craft cloth, 100% cotton, natural color, maufactured by James Thompson & Co. Inc. in New York City (mill is in Greenwood, Delaware). Part number is 103293. It looks like cheesecloth treated with starch or a starch like material. Its special quality is that when wet, it is somewhat shapless, but when dry and stiff again, it takes on the shape of whatever object it was attached to.
It appears that James Thompson no longer makes this material.
Woodland Scenics has plaster cloth. I recently found an online art supply store that has it at a cheaper price.
I cut and lay the dry strips in place, then spray with a water bottle. Light pressure with your fingers works it into place and around things and to fill in the holes, as this is really just plaster impregnanted gauze. Slighty overlap each piece, let dry and you have a nice solid base. I love the stuff. http://www.dickblick.com/
If you have a medical supply store nearby, you might be able to find plaster-impregnated cheesecloth used for body casts. This is identical to the product sold by Woodland Scenics. I have never heard of the Wet & Shape material, which must have been a regional product sold only in New England.
I wonder if regular cheese cloth dipped in diluted white glue would have most of the desires characteristics? I remember a version of hard shell years ago in MR where the guy took swatchs of old bed sheets dipped in diluted white glue for his mountains and hills.
Dave Nelson
Handi-Wipes cleaning cloths work well, too, and are very strong when wet. Paper towels sometimes get soggy and fall apart, expecially the cheaper brands. The Bounty towels are very strong themselves. Buy whatever is cheapest!