1. GREENHOUSE GLAZINGS Glass Film Plastic Rigid-Panel

2. GLASS Float-1/8” double strength common in US Light Transmission: Single Layer = 88%-94% Double Layer= 77% High air filtration High thermal conductivity Lower relative humidity $2.00-$7.00 ft 2 Low impact resistance Life Span = 25+years

3. PLASTIC FILMS Polyethylene Vinyl Polyvinyl Fluoride Polyester Tefzel

4. POLYETHYLENE Major film used in the US 6-mil exterior / 4-mil interior layers (double layer for insulation) UV inhibitors increase life span; 3 to 4 year life Antifog materials = less condensation problems IR blockers = less heat loss PLASTIC FILMS

5. POLYETHYLENE Costs (per layer) 6¢/ft 2 for 3-year film (UV inhibitor added) 7¢/ft 2 for 3-year + antifog 8¢/ft 2 for 3-year + IR blocker 9¢/ft 2 for 3-year + antifog + IR blocker Labor to recover = 12¢/ft 2 to 23¢/ft 2 of ground area covered by greenhouse (not of roof area) PLASTIC FILMS

6. VINYL Polyvinyl Chloride 8 and 12 mil films (4 and 5 year life) 21.5¢/ft 2 for 12 mil Static charge is bad Used in Japan PLASTIC FILMS

7. POLYVINYL FLUORIDE Tedlar 95¢/ft 2 for 4 mil / 2 mil tube PLASTIC FILMS

8. POLYESTER Mylar Too expensive for glazing but is used for shade cloth material PLASTIC FILMS

9. TEFZEL T 2 Ethylene tetrafluoroethylene Should last 20 years 95% light transmission for single layer 91% light transmission for double layer More IR loss than polyethylene $1.20/ft 2 (but lasts 20 years) Use limited by 50-inch width limit right now PLASTIC FILMS

10. RIGID-PANEL Polyvinyl Chloride Fiberglass-Reinforced Plastic (FRP) Acrylic and Polycarbonate

11. POLYVINYL CHLORIDE (PVC) Has been phased out for the most part 2+ year life span 4x the cost of polyethylene film Light exposure = dark and brittle RIGID-PANEL

12. FIBERGLASS-REINFORCED PLASTIC (FRP) more popular in past 5-20 yr. life expectancy, depending on grade panels flexible enough to conform to the shape of quonset frames transmits 88-90% PAR -$1.00 ft 2 RIGID-PANEL

13. FIBERGLASS-REINFORCED PLASTIC (FRP) more resistant to breakage than glass light distribution more uniform than glass because less expensive to cool (20% less than glass) fewer structural members than glass FRP surface subject to etching by dust abrasion glass lasts indefinitely, FRP may last half lifetime of grower RIGID-PANEL

14. ACRYLIC AND POLYCARBONATE Double or triple-layer 10 yr. Life Often coated to prevent condensation drip; acrylic coating on polycarbonate slows UV degradation RIGID-PANEL Corrugated Polycarb

15. ACRYLIC AND POLYCARBONATE Used for glazing side and end-walls 8mm-16mm thick, thinner can be bent, thicker cannot Acrylic-83% PAR; Polycarbonate-79% PAR Acrylic-$2.10 ft 2 Polycarbonate-$1.60 ft 2 RIGID-PANEL Acrylic