I am going to buy more 10 mil plastic to do my 3 big windows , I used 10 mil poly over the sliding glass doors wood trim frame , giving me 4" of air space on one side and two inches on the other half.
The Quilt / Comforter I tacked up adds 3 to 4 R value and increased U factor with its synthetic fill.
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Here is a pdf on the savings possible with window treatments complete with the Math to expose the true savings and improvements.
http://learningstore.uwex.edu/assets/pdfs/B3064.pdf
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bonus content !
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R-Values (per inch)
Concrete = 0.10
Stone = 0.10
Brick = 0.35
Hardwood = 0.90
Softwood / plywood = 1.2
Particle board = 1.85
Insulating board = 2.60
Sidings = 1.00
Brick = 0.35
Asphalt shingles = 0.44
Wood shingles = 0.94
Built-up roofing = 0.90
Rock wool = 3.70
Mineral wool or fiber batt = 2.90
Cellulose = 3.70
Lightweight aggregate concrete = 2.00
Cement board = 2.30
Stucco / plaster = 0.20
Gypsum / plaster board = 0.90
Fiberglas = 3.16
Fiberboard = 3.45
Polystyrene extruded = 5.40
Polystyrene expanded = 4.35
Polyurethane foam = 7.70
Building paper / felt = 0.06
Cork = 2.00
Ceramic tile = 0.15
Vinyl / linoleum / rubber tile = 0.64
Synthetic carpet (level loop) = 5.90
Synthetic carpet (plush) = 4.50
Wool carpet = 4.50
Fiber / hair / jute cushion = 3.88
Flat rubber cushion = 2.72
Rippled rubber cushion = 1.82
Prime urethane cushion = 4.44
Bonded urethane cushion = 3.96
Solid wood door = 1.56
Single glass window = 0.8
nsulating double glass = 1.89
Energy plus double glass = 4.50