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4mm vs 6mm Polycarbonate Greenhouse Panels: Which is Better?

4mm vs 6mm Polycarbonate Greenhouse Panels: Which is Better?

When it comes to polycarbonate glazing for a greenhouse, one of the most important decisions is choosing the right thickness. The two most common options are 4mm and 6mm polycarbonate panels. But which thickness is the best choice for your greenhouse?

In this in-depth guide, we will compare 4mm vs 6mm polycarbonate greenhouse panels to help you determine the right thickness for your specific needs and climate.

Key Takeaways

  • Polycarbonate is extremely strong, durable, and shatterproof, making it ideal for greenhouses. Both 4mm and 6mm provide robust protection.

  • 6mm polycarbonate has a higher R-value (1.54) than 4mm (1.43), giving it 25-50% better insulation properties. This helps retain heat in colder climates.

  • 4mm polycarbonate transmits 5-10% more light. It's better for maximizing light in warmer climates.

  • 6mm panels are more impact-resistant and have greater longevity, especially for large greenhouses. They better withstand snow, hail, and wind.

a side by side image of polycarbonate sheets and greenhouse

    Benefits of Polycarbonate Greenhouses

    Before diving into the differences between 4mm and 6mm, let’s first look at why polycarbonate is an ideal glazing material for greenhouses in the first place.

    Some of the key advantages of polycarbonate greenhouse panels include:

    • Impact Resistance - Polycarbonate sheets are virtually unbreakable. They are 200 times stronger than glass and 30 times stronger than acrylic. This makes them highly resistant to hail, falling branches, and other impacts.

    • Lightweight - Polycarbonate panels are much lighter than glass. This allows for easier installation and may reduce structural support requirements.

    • Insulation - Multiwall polycarbonate provides excellent thermal insulation thanks to the air gaps between the walls. This helps regulate interior greenhouse temperatures.

    • Light Diffusion - The translucent panels diffuse sunlight, improving light distribution and reducing shadows inside the greenhouse.

    • UV Protection - Polycarbonate blocks over 99% of harmful ultraviolet radiation, protecting plants and people inside.

    • Affordable - Polycarbonate glazing is generally more economical compared to glass greenhouses.

    With these benefits in mind, let’s look at how 4mm and 6mm polycarbonate panels compare.

    Key Comparison Between 4mm and 6mm Polycarbonate Panels


    The main difference between 4mm and 6mm polycarbonate lies in the thickness of the panels, as the names imply:

    • 4mm Polycarbonate - Each panel is 4 millimeters thick. This is the common thickness for polycarbonate sheets used in greenhouses.

    • 6mm Polycarbonate - Each panel is 6 millimeters thick, making it 50% thicker than 4mm polycarbonate.

    Now let’s look at how thickness affects other performance factors.

    Strength and Durability

    When it comes to strength, polycarbonate outperforms glass by leaps and bounds. It provides significant durability advantages:

    • 200x Stronger Than Glass - Polycarbonate has around 200 times the tensile strength of standard glass. It is virtually unbreakable under normal conditions.

    • 250x Impact Strength of Glass - The high impact resistance makes polycarbonate panels extremely resistant to weather events like hail, falling branches, heavy snow loads, and more. Both twin-wall and triple polycarbonate provide excellent impact protection.

    • Shatterproof - Unlike glass, polycarbonate does not shatter on impact. It bends and flexes instead of breaking.

    • Hail Resistant - Polycarbonate can withstand hailstones up to 1 inch in diameter. It prevents costly damage from intense storms.

    • Heavy Snow Loads - Multi-wall polycarbonate can bear heavy snow loads up to 100 PSF (pounds per square foot) without buckling.

    While both thicknesses provide robust protection, the extra 2mm gives 6mm polycarbonate a slight edge in strength and durability. But both are remarkably hail and shatter-resistant.

    Insulating Properties

    Insulation is another key performance area where the thickness makes a difference.

    The insulation value of panels is measured using the R-value:

    • Higher R-Value = Better Insulation - R-value indicates how well a material prevents heat transfer. Higher R-values provide greater insulation per inch.

    Here are the typical R-values for 4mm vs 6mm polycarbonate:

    • 4mm Polycarbonate - 1.43

    • 6mm Polycarbonate - 1,54

    As you can see, the extra 2mm thickness boosts the R-value significantly. This means 6mm polycarbonate provides around 25-50% higher heat insulation.

    Beyond R-value, other insulation factors include:

    • Air Gaps - The multiple internal walls trap air, creating insulated pockets. More walls increase insulation.

    • Light Transmission - Thicker panels transmit slightly less light. This further helps maintain interior temperatures.

    • Thermal Mass - Thicker polycarbonate has higher thermal mass, absorbing more solar energy during the day.

    Together, these enhancements give 6mm polycarbonate a notable advantage for insulating greenhouses in cold climates.

    Light Transmission

    Light transmission is vital for plant growth. Polycarbonate provides excellent light diffusion thanks to its translucent, multiwall design.

    The 4mm polycarbonate transmits around 5-10% more natural light. However, both thicknesses still maintain excellent light transmission for greenhouses.

    And while 6mm polycarbonate transmits less light, it also better diffuses and spreads light evenly throughout the greenhouse. This prevents dark corners or shadows.

    Cost Comparison

    While 6mm polycarbonate panels are generally more expensive than 4mm ones due to the extra material, they offer better thermal insulation, potentially leading to energy savings over time. However, costs can vary based on factors like supplier, region, and market conditions.

    It's recommended to conduct a detailed cost-benefit analysis considering factors such as greenhouse size, local climate, and heating/cooling costs before making a decision.

    Here is an overview of key comparisons:

    Thickness 4mm 6mm
    Strength Very high Slightly higher
    Impact Resistance Extremely high Slightly higher
    Insulation (R-value) 1.43 1.54
    Light Transmission Higher by 5-10% Lower
    Cost Lower Higher
    an actual product image of the Hoklartherm Riga Greenhouses 5 with flowers outside

    Best Uses for 4mm vs 6mm Polycarbonate

    With all the factors above considered, here are some general recommendations on the ideal uses and climates for 4mm vs 6mm polycarbonate greenhouse glazing:

    Best Uses for 4mm Polycarbonate

    • Small to mid-size hobby greenhouses up to 200 sqft
    • Warm, sunny climates that rarely freeze
    • Using supplemental greenhouse heating
    • Budget-friendly option to maximize light transmission

    Best Uses for 6mm Polycarbonate

    • Large commercial greenhouses over 300 sqft
    • Cold climates prone to heavy snow, hail, and frigid temps
    • Unheated greenhouses reliant on passive solar
    • Regions with frequent intense weather events
    • Greenhouses are expected to last over 10-15 years

    These are general guidelines only, and you should consider your specific climate and needs. Many factors like budget, structural support, and desired light transmission also play a role.

    Key Considerations When Choosing Between 4mm vs 6mm Polycarbonate

    If you're trying to decide between 4mm vs 6mm polycarbonate panels, here are some of the key factors to consider:

    • Climate and Location - In colder climates, 6mm provides better thermal insulation to retain heat in an unheated greenhouse. In hot climates, 4mm maximizes light transmission.

    • Greenhouse Size - For larger greenhouses, the stronger 6mm thickness can better withstand snow and wind loads. twin-wall polycarbonate suits smaller hobby greenhouses.

    • Budget - 6mm has a higher upfront cost but can save on heating expenses long-term. 4mm is more budget-friendly initially.

    • Structural Support - Using 6mm may require additional framing to handle the increased weight load per square foot.

    • Lifespan - 6mm thickness equates to greater impact resistance and longevity, while 4mm has a shorter lifespan.

    • UV Exposure - In areas with intense sunlight, 6mm maintains light transmission and clarity better than 4mm over time.

    • Heating Usage - Unheated greenhouses benefit most from the superior insulation of 6mm polycarbonate panels.

    a product image of the interior of the Solexx Conservatory 16x20x96 - DELUXE


      By understanding the performance differences, you can make the ideal thickness selection for your specific greenhouse needs and environment. With smart polycarbonate glazing choice and proper installation, you can enjoy the benefits of a durable backyard greenhouse for many years to come.


      What thickness of polycarbonate sheet is best for a small greenhouse?

      For small greenhouses, a twin wall polycarbonate sheet is usually sufficient. It is lightweight and easy to install while providing a decent level of insulation. However, if you plan on heating your greenhouse during the colder months, a 6mm polycarbonate would be a better choice due to its higher insulation factor.

      Why is a thicker polycarbonate sheet better for insulation?

      The thickness of polycarbonate affects its insulation properties because thicker sheets have larger air pockets trapped between them. This creates a better thermal barrier, reducing heating costs and maintaining a more consistent temperature within the greenhouse.

      Is a 10mm polycarbonate sheet a good choice for a greenhouse?

      A 10mm polycarbonate sheet can be a great choice for a greenhouse if it's located in a colder climate or if you plan on using a heater in it. It provides excellent insulation, keeping the interior warm even in cold weather. However, keep in mind that it allows less light transmission compared to thinner sheets.

      Which type of polycarbonate sheet is best for a wall polycarbonate?

      For wall polycarbonate, a triple wall polycarbonate sheet is most commonly used. The choice ultimately depends on the specific requirements and the climate of the area. These are lightweight, easy to install, and provide good insulation.

      What thickness of polycarbonate should be used for a greenhouse in a cold climate?

      For a greenhouse in a cold climate, a thicker polycarbonate sheet is recommended. Considering insulation needs and heating costs, a 10mm to 16mm polycarbonate sheet would be ideal. It offers the necessary insulation to keep the interior of the greenhouse warm.

      Previous article Buying A Greenhouse: A Guide To Choosing The Best Greenhouse
      Next article Glass vs Polycarbonate Greenhouses: Which is Better for Your Growing Needs?

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      About The Author

      Andy Wu - Resident Expert

      Andy Wu - Resident Expert

      Andy Wu is the resident backyard products expert and hails from Atlanta, Georgia. His passion for crafting outdoor retreats began in 2003.

      As a fellow homeowner, he founded Backyard Oasis to provide top-quality furnishings and equipment, collaborating with leading manufacturers.

      His main focus is on sheds and generators!

      In his spare time he like to hike the tallest mountains in the world and travel with his family.

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