An internal flexible dust seal for connecting and accomodating misalignment, expansion, contraction, and torsion between openings of adjacent ducts carrying dust and particulate laden hot gases. The internal flexible dust seal can undergo lateral, axial, angular, and torsional movements while at the same time keeping any particulate matter or dust from leaving the duct and/or entering the space between liner plates and the insulation cavity of an outer gas flexible seal or expansion joint. The internal flexible dust seal is fixed to the inside of the duct.