Phlex-glue

[derekleffew]

A PVC-based white adhesive, similar to Elmer's or Sobo. Often used as a paint adhesive, or can be used as a binder with dry pigment for making one's own paint, if a shiny finish is desired. Can also be used as a gloss medium.

One brand:

http://www.rosco.com/us/scenic/flexbond.cfm

From http://www.mochi-mochi.org/workshop/crafting/locker/adh/fglue.html :

This is, as the name implies, glue that remains somewhat flexible after it has dried. You shouldn't expect it to be as resilient as cloth, but you can get some interesting effects with this stuff. Common applications include using it to bind pigment to surfaces that normally resist paint, coating surfaces that have a tendency to "shed" (like foam rubber), or embedding surface details (like sand or glitter).
Common brands include Flex Bond and Phlex-Glue. Pre-mixed, it looks like slightly runny white / PVA glue. You can also buy it in powdered form. If you want to find it in smaller quantities or can not get it from a theater supply company, try a store that sells stuff to bookbinders: Daifuku Mochi is more familiar with this under the name of "bookbinder's glue".