Pour-down insulation mix is a concrete compound shipped to you in dry form. To use, simply mix with water and pour down the void between the chimney liner and the inner chimney wall. Pour-down mix is used primarily in applications where space is tight and an insulation wrap will not fit.
Insulating a liner for use with gas or oil appliances is optional. However, liners for solid fuel appliances MUST be insulated.
An average liner installation will require 3-4 boxes of mix.