Depending on the job, commercial or residential, there may be a need for fiber glass acoustical lining on the inside of the duct work. Duct liner, in it’s simplest form, is there to help reduce noise and provide a minimal R-value—much less than duct wrap—to provide more consistent temperatures and energy efficiency.
K&E Sheet Metal’s morning was full of duct liner, one inch thick to be exact. The thickness can range from 1/2” to 2”. Our shop mostly deals with half-inch and one-inch. Occasionally, we will get a spec (specification) for 1 1/2” or 2”, but it’s rare for the size jobs—commercial vs. Industrial— we fabricate for. In future, as the shop grows, that could change.