Flexible greenhouse covers are often referred to with the general term of “poly film”. Not all covers are made from polyethylene materials. It’s important to compare various products on more than just their claims of durability and measured thickness. While it’s true that 6 mil greenhouse film is the industry standard for multi-year use, there are products offering greater durability than others at that particular thickness. Find out what else you need to know to accurately compare your options for a covering.
PVC, Polyethylene, or Something Else
You’ll find many commercial greenhouse films only labeled as a vague poly material. This term usually refers to polyethylene, but many products labeled in this way are actually made from PVC. Since PVC stands for polyvinyl chloride, it’s still technically correct to use the poly term to describe these products. PVC is heavier than polyethylene for the same thickness, slowing down and complicating installation for the largest structures. Polyethylene is also much less likely to crack in cold weather than PVC, especially reinforced materials with woven cores.
Polyethylene films also come in various formulations that vary in their benefits. The best greenhouse covers combine multiple types of polyethylene are layered together. BTL Liners’ ArmorClear is a great example because it combines both high density polyethylene (HDPE) and low-density polyethylene (LDPE) to take advantages of their unique benefits. It’s also a reinforced product with a woven inner layer to resist punctures and tearing over years of use.
Reinforced or Non-reinforced
Reinforced greenhouse covers tend to cost a little more per square foot due to the slightly more complex manufacturing process. Unless you plan to install new layers of film every year or two, you’ll want the extra wear and tear resistance of a reinforced product. Woven fibers are embedded in the center of two or more layers of polyethylene material to keep rips from spreading if something does break through the plastic. Non-reinforced films are less expensive, but they’ll need far more patching and repairs through the year and faster replacement. Greenhouse films tend to wear out wherever they’re stretched or wrapped over a sharp edge. The film moves slightly back and forth with wind and rain, resulting in a lot of wear at the edges. Reinforced covers are much better at handling this issue without damage.
You’ll generally find greenhouse films guaranteed for use for one, two, or up to six years for highly reinforced products. A lifespan of only one to two years may seem short, but those films tend to be very affordable and a good option for emergency cover when there’s major damage. If you’re looking for a long-term cover for your greenhouse, make sure to choose a product warrantied for at least three to five years. These films are thicker and offer better UV resistance to prevent the plastic from growing brittle and fragile over time. BTL’s ArmorClear cover, offers high UV resistance, optimal light transmission rates, durability and easy installation, while boasting a life span exceeding a decade; making it one of the best products on the market.
While you do want some amount of UV light to penetrate through your film, especially if you’re planning to pollinate with honeybees, most films are designed to reflect as much of it as possible. This is because materials that absorb UV rays typically become brittle over time, increasing the chances of a rip or tear developing in the film. High levels of UV resistance allow poly films to last much longer, especially when they’re not covered with shade cloths for the summer. Polyethylene materials are naturally more UV resistant than PVC, but this can vary depending on what’s added to the specific film during manufacturing.
Light Transmission Rates
Most greenhouses benefit from films with the highest possible light transmission rates, especially those holding flowering plants and tender seedlings. High quality films can transmit 80 to 90% of the available light without sacrificing durability or UV resistance. Finding a clear enough film is often what determines if a greenhouse will need supplemental lighting or not. Relying on natural sunlight as much as possible is essential for maximizing profits by minimizing energy costs. Films also offer high rates of diffusion, that scatter light, so more of it is absorbed through the undersides of leaves. This increases growth rates while reducing the risk of sun scalding; a common problem with clear glass panels.
Double and triple layers of poly film offer a surprising amount of insulation to prevent heat loss. You can go one step further by installing an infrared (IR) blocking film layer inside of the structure or by spraying on a coating on the film you choose. IR films keep heat from radiating out through the poly film overnight, keeping more heat inside the greenhouse where you need it. This is one of the most effective major upgrades to improve profitability in your greenhouse if you’re growing through the winter with supplemental heating.
You should feel prepared to choose between the many greenhouse covers on the market now that you’ve explored the facts about materials, light transmission, and durability. If you’re still wondering how to choose the right cover for your particular greenhouse, we can help here at BTL Liners. Our years of experience working with greenhouse owners have given us the knowledge to pick the right material for every project.