Greenhouse Glazing Makes the Greenhouse

Backyard Gardening Fb 30

Greenhouse Glazing Makes the Greenhouse

Greenhouse glazing (greenhouse covering) lets the sunlight in while trapping warmth inside.

And that, after all, is what makes a greenhouse work.

If you’re a greenhouse gardener, light is your most precious resource.

In the low light days of winter, there’s just barely enough light to give many plants what they need (this varies, of course, depending upon your latitude).

But heat is also crucial.

A greenhouse must be able to trap heat inside that is generated by the sunlight entering the greenhouse.

That’s free heat, and without it a commercial greenhouse could not be viable, and a hobby greenhouse exorbitantly expensive. 

Greenhouse Glazing Makes the Greenhouse

So a perfect form of greenhouse glazing would allow sunlight to enter completely unimpeded while maintaining heat within the greenhouse with 100% efficiency.

There is no ‘perfect’ greenhouse glazing, of course. But the most commonly used glazing materials can be quite effective. 

The glazings listed below are the most popular and most commonly used greenhouse coverings. They aren’t the only types of greenhouse coverings in use, of course.

Translucent fiberglass panels, for example, are used to some degree as a greenhouse glazing. But fiberglass panels have some problems (such as yellowing caused by sunlight) that make them less popular as a greenhouse covering.

Similarly, other materials that are used for covering greenhouses have some deficiency or obstacle (such as high cost) that prevents them from gaining widespread acceptance as a greenhouse glazing material.

The following, then, are the most commonly used materials. It’s likely that one of them is the very best choice for your greenhouse. 

  • Polyethylene Film
    Greenhouse plastic film is easily the least expensive method of covering a greenhouse. But greenhouse poly film, if used correctly, is also quite effective. In addition to cost savings, using polyethylene film to cover your greenhouse will provide other benefits – and some drawbacks, as well. Click here to read more about greenhouse plastic film
  • Polycarbonate Panels
    Greenhouse polycarbonate is a very recent advancement in greenhouse covering technology. Polycarbonate panels are very light, very strong, and offer a high projected service life. But yes, polycarbonate greenhouses do come with some disadvantages of their own. Click here to read more about greenhouse polycarbonate
  • Glass Panels
    Greenhouse glass panels have been in use for centuries, from the very beginning of greenhouse history. Until recently, glass greenhouse panels were the only type of greenhouse coverings available. But a glass greenhouse is far from just an antique throwback. Click here to read more about greenhouse glass

The Most Important Criteria for Greenhouse Glazings

When you’re deciding upon the type of glazing for your greenhouse, there are many considerations. And some have little to do with the actual performance of the glazing.

For instance, the appearance of your greenhouse might be of great importance to you. Perhaps only certain greenhouse coverings will conform to ‘the look’ you have in mind for your greenhouse. Or perhaps cost will be an overriding factor in your decision.

But the following considerations have the most impact upon the performance of a greenhouse, and the cost and effort required to build, maintain and heat it. Here’s how the 3 most commonly used greenhouse coverings stack up against each other:

Light Transmission (as % of light allowed to pass through)

  • Polyethylene Film: around 90% for single-layer, around 85% for double-layer
  • Polycarbonate Panels: around 90% for corrugated, around 80% for twinwall
  • Glass Panels: around 90%

Insulating Ability (as “R” factor: higher number = better insulating properties)

  • Polyethylene Film: .83 for single-layer, 1.43 for double-layer
  • Polycarbonate Panels: .83 for corrugated, 1.64 for twinwall
  • Glass Panels: .91


  • Polyethylene Film: Not particularly strong, but flexibility permits poly film to stand up to strong winds, and even impacts as severe as small hail (if not larger than pea sized).
  • Polycarbonate Panels: Possess high impact resistance. The strongest of these 3 types of greenhouse coverings.
  • Glass Panels: This one’s obvious, isn’t it?


  • Polyethylene Film: 1 to 5 years depending upon UV resistance and thickness.
  • Polycarbonate Panels: 10+ years.
  • Glass Panels: Can potentially last for decades if not assailed by hailstorms, little boys with stones, errant baseballs, etc.

What’s the Best Greenhouse Glazing for Your Greenhouse?

The answer, of course, is that it depends.

It depends upon the look you want for your greenhouse. It depends upon your climate and what you’ll be growing in your greenhouse. It depends upon conditions your greenhouse will endure (high winds, high snow loads, high risk of hail). And for most of us, it also depends upon our budget.

The good news, though, is that when choosing a greenhouse covering for your greenhouse, it’s hard to make a really bad choice. Because in truth, all of the commonly used greenhouse coverings are quite effective.

But by understanding the strengths and weaknesses of each, hopefully you’ll be able to choose the very best greenhouse covering for your situation. 

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