Plexiglass is a common brand name for acrylic sheeting, a plastic polymer known as Poly(methyl methacrylate) (PMMA). Acrylic offers a clear, durable alternative to traditional materials, making it a popular choice for both hobby and commercial greenhouse growers. This modern glazing option can certainly be used for a greenhouse, providing a number of advantages. However, its application involves specific trade-offs when compared to glass or other polymer alternatives, requiring careful evaluation.
Horticultural Performance of Acrylic Sheeting
The performance of acrylic sheeting is defined by its superior optical and thermal properties, which directly influence the environment for plant growth. Standard acrylic panels transmit an exceptionally high amount of photosynthetically active radiation (PAR) to the plants below. This high light transmission ensures that plants receive the energy they require for robust photosynthesis, particularly during periods of lower sunlight intensity. This clarity is comparable to, and often exceeds, that of traditional horticultural glass, with transmission rates reaching up to 92% or more of visible light.
The material naturally blocks most of the harmful ultraviolet (UV) spectrum, which helps prevent cellular damage in plants and material degradation over time. Some specialized acrylic sheeting is available that allows UV light to pass through, which is sometimes beneficial for specific crops or insect control.
Acrylic also provides better thermal insulation than single-pane glass, which is a significant advantage for managing heating costs. When used in multi-wall configurations, such as twin-wall sheets, acrylic can achieve an R-value around 1.8, effectively trapping heat inside the structure. The material is also highly impact-resistant, being approximately 10 to 17 times stronger than glass, offering protection against hail and wind-blown debris.
Comparing Acrylic to Other Glazing Materials
Choosing a greenhouse glazing material requires balancing initial cost, long-term durability, and structural requirements, which places acrylic between its two main competitors: glass and polycarbonate. Acrylic is generally a cost-effective option for a durable glazing material, often priced lower than polycarbonate and significantly less than specialized tempered glass. Its relatively lighter weight—about half that of glass—reduces the structural load on the greenhouse frame, potentially lowering the overall construction expense.
Acrylic’s primary advantage is its long-term optical clarity; it resists the yellowing that can plague other plastics over time. Manufacturers often offer warranties up to 30 years against significant degradation. Traditional glass offers the longest potential lifespan (40+ years), but it is heavy and requires a substantial frame, increasing construction complexity and cost. Glass is also prone to shattering, creating a safety hazard.
Polycarbonate, while often slightly less clear than acrylic with light transmission around 88%, is the most impact-resistant of the three, being up to 250 times stronger than glass. Standard polycarbonate typically has a shorter lifespan, often around 20 years, and requires a UV-resistant coating to prevent yellowing. Therefore, acrylic provides a valuable middle ground. It offers near-glass clarity and durability without the weight and fragility of glass or the lower clarity and shorter lifespan of some polycarbonate options.
Installation and Long-Term Care
The installation of acrylic sheeting is simpler than glass due to its lighter weight, but it requires careful attention to the material’s unique physical properties. Acrylic exhibits a relatively high rate of thermal expansion and contraction in response to temperature changes. Panels must be installed using specialized fasteners and framing systems that allow for adequate movement within the frame, preventing buckling or cracking. Failing to account for this expansion can lead to structural stress and panel failure over time.
Long-term maintenance primarily involves careful cleaning to preserve the sheet’s clarity. Acrylic is more prone to surface scratching than glass, so abrasive cleaners, ammonia-based products, or rough scrubbing pads should be avoided. The recommended cleaning method is a soft cloth or sponge with a mild soap and water solution. While acrylic is known for its UV stability and resistance to yellowing, regular inspection is beneficial for identifying minor damage or accumulated dirt that could reduce light transmission. The material’s resilience means it does not shatter, but any deep scratches or cracks should be addressed promptly to maintain the greenhouse’s thermal efficiency and structural integrity.