I have seen the covers to be of two kinds. Glass and transparent white polythene sheet.

Google search will show more material which are used as greenhouse cover.

The main purpose of greenhouse covering to use a material which covers the greenhouse frame and plays a key role in heat retention. The most widely used materials are polycarbonate and polyethylene film. You may also use Glass, Fiberglass, Acrylic and Vinyl. Glass has been the traditional green house covering material but it is poor insulator. I think, polycarbonate is very good as it is very strong and light weight material.

Each one has its advantages and disadvantages regarding light transmission, heat insulation, flexibility, physical endurance, heat endurance, weight and cost. There is no perfect material for all of those aspects. Depend on your specific situation you can choose one that fits the best. You can find more information about this in many books about greenhouse like "Greenhouse Technology and Management" by Nicolass Castilla which has a whole chapter dedicated to covering materials.

Dear @ Subir Bandyopadhyay. I'm thankfull for your answer. I want to know how it's the best regarding it s thermal efficiency and its cost. Maybe an materiel can be perfect but when it's expensive it can't be using.

Codially

Dear Ali

I think plastic is a reasonable solution for developing countries. It is available in the markets and not expensive.

Your main problem is the heat losses:

- choose a plastic with a rather large thickness;

- the greenhouse side not hit by solar radiation, must be covered by another insulating material (non-transparent). like that you reduce heat losses.

Dear @J. C. Tarafdar thank you very much for your answer and your interesting of this subject. I want only to ask you for plyvarbonate as greenhouse materiel mybe so expensive of the simple agricultur. I think it's better regarding its insolation and time of using . Thanks again

Dear @ Duy Minh Pham. Thank you for your interesting answer. I agree that each material have its advantageous and disadvantageous, but in industral area we should choise the best material which is adequate to our using. I will read the book of Nicolass Castillo. Thank you dear very much.

Dear @Abdelrahmane.

I'm very glad of reading to you. As usually you are a simple man that give the simplest solutions. I'm thankfull for your interesting of my project and my question. Your solution of material using is perfect from cost, but you know dear plastic have a low preriod of using and no good for region of strong wind. Thank you again dear

Daer Ali,

In your subject you have two problems

- Heat production (there are solutions).

- Reduction of heat loss (no efficient solutions) - here it is a bit complicated

but it is not impossible to find a solution-

Give me a little time and I will send you the solutions

Polythene sheets seem to be cost effective because I have seen even small nurseries using it.

Thank you dear Prof. Subir Bandyopadhyay for your interesting information. can I ask do you have using this material for similar application?

Ok dear Dr. Abderrahmane, take your time, I will waiting you. Thanks a lot

In practical application mostly 3 aspects are considered among those I mentioned: cost, weight and endurance. These aspects all come down to cost efficiency. For example glass has strong endurance, giving it a long use time, but it's more expensive and its weight requires a stronger and more costly greenhouse framework. Therefore glass is only used for greenhouse with long intended use time (> 10 years) or in areas with severe weather (heavy snow, strong wind, etc.) that plastic cannot be used.

Heat insulation, although important, isn't usually considered when choosing a covering material, because covering materials do not differ much regarding heat insulation, and there are multiple ways to compensate for it. For example in Korea where I am studying with very cold night, they simply use another 1 or 2 layers of insulating plastic and cover the greenhouse at night. This is automated with timer and motor, and even with several plastic layers is still quite cheaper and much more efficient than using another covering material like glass. In fact in tropical country where temperature differs a lot between day and night it is a better option because you can change the greenhouse heat insulation during the day instead of having a fixed heat insulation.

Light transmission sometimes comes into consideration, and in areas with very low sunlight it might be preferred to use glass, although the difference is not very big. Light transmission of plastic reduces over time, but within 2-3 years it is almost negligible. Dust is more of a problem, especially in area with little rain. Unlike glass, plastic has the tendency to attract dust due to its static charge, and requires frequent cleaning if there is no rain. However, there are some special type of plastic with anti-charge surface which might be useful in such case.

Dear Duy Minh Pham ;

thank you very much for this answer which you gave the necessarily for the use of a material in a greenhouse.

Indeed, as you mentioned all the effects are compute to have a better efficiency.

thanks again