Or did we have a chimney fire and not know it? An exploratory look and cleaning today showed nothing in the liner (sorry no pic's - camera died) but a fluffy, black crispy thin layer of dried creosote foam. It brushed out real easy. Previous two years with un-insulated singlewall liner we got BAD stage-3 glazed creosote buildup in the liner, but only in the upper 9 feet where it's inside the chimney in unheated space (attic). That glazed hard shiny stuff was near impossible to remove. The SS runs through a clay-lined masonry chimney with inside dimensions of 6 1/2 X 10 1/2 inches. This season, the liner is insulated with perlite. Poured perlite down the entire length of the 25' vertical flue. We've only burned a dozen times this year, but have made HOT fires and the wood is seasoned right. Could the higher upper flue temps, because the flue is now insulated, have 'fluffed' the leftover glazed creosote from last March cleaning? Or is it possible there was a flue fire?