Polyethylene (PE) glazing, often referred to as poly film or plastic sheeting, is a widely adopted material for covering modern greenhouse structures. This flexible polymer provides a lighter and more adaptable alternative to traditional rigid glazings like glass and multi-wall polycarbonate panels. Its popularity stems from its ability to create a protective, controlled environment suitable for a wide range of commercial and hobby growing operations. PE film offers specific economic and horticultural benefits that address the needs of many growers.
Low Cost and Affordability
Polyethylene film is the most budget-friendly option for initial greenhouse construction. The material’s cost per square foot is significantly lower than that of both glass and rigid polycarbonate sheeting, making it highly accessible for large-scale commercial projects and small-scale hobbyists.
The lightweight nature of PE film also translates directly into reduced construction costs. Unlike heavy glass, which requires a robust, high-load-bearing frame, polyethylene can be supported by a simpler, lighter-duty structure. This decreases both the material costs for the frame and the labor expenses necessary for assembly. Although the film needs replacement every few years due to UV degradation, the minimized initial investment offers a substantial financial advantage.
Simple Installation and Material Safety
The physical properties of polyethylene film greatly simplify the installation process compared to rigid materials. PE film is lightweight and flexible, often supplied in large rolls that can be quickly unwound and secured over the greenhouse frame. This flexibility allows the film to conform easily to the curved shapes of hoop houses and tunnels, which is difficult or impossible with flat, rigid panels.
Installation methods are straightforward, often involving simple fastening systems like metal channels or snap clamps. This process is less labor-intensive and requires fewer specialized tools than fitting heavy glass panes or multi-wall panels. Furthermore, PE film significantly enhances safety; unlike glass, it does not shatter into dangerous shards, eliminating the risk of sharp debris during installation or after severe weather events.
Light Diffusion and Plant Health
One significant horticultural advantage of polyethylene glazing is its capacity for light diffusion. Specialized PE films scatter the light evenly across the growing space, rather than permitting direct, concentrated beams of sunlight. This diffusion prevents the formation of intense hot spots and shadows that can cause plant scorching and irregular growth patterns.
The scattered light penetrates deeper into the plant canopy, reaching lower leaves that would otherwise be shaded. This increases the total amount of photosynthetically active radiation (PAR) absorbed by the plant, leading to more efficient photosynthesis and higher yields. Growers using diffused films have reported increases in crop yields, sometimes ranging between 30 and 40 percent.
Modern PE films can also be manufactured with specific additives to filter the light spectrum. For example, UV-transparent films allow ultraviolet light through, enhancing color and flavor development in certain crops. Conversely, some films block UV light entirely, which limits the severity of certain fungal diseases, such as downy mildew.
Superior Heat Retention
Polyethylene glazing offers excellent thermal performance when utilized in a double-layer inflated system. This setup involves securing two layers of PE film over the frame and using a blower fan to maintain a constant cushion of air between them. The resulting air pocket acts as an insulating barrier, which significantly increases the material’s R-value (a measure of thermal resistance).
This inflated air space drastically minimizes heat loss through conduction, especially during cold nights. Compared to a single layer of film, a properly inflated double-poly system can reduce heating fuel consumption by over 40 percent, leading to substantial energy savings. The stabilization of internal temperatures also protects plants from sudden fluctuations, promoting consistent growth.
To further enhance heat retention, growers can opt for films containing infrared (IR) additives, often called thermal films. These films are engineered to trap long-wave infrared radiation, which is the heat naturally emitted by the soil and plants at night. When used as the inner layer of a double-poly system, these IR films can provide an additional 15 to 20 percent in energy savings.