I. Classification of Greenhouse Films
1. Polyethylene (PE) Film
*Market Share: The lowest-cost entry-level choice, holding more than half of the market share.
*Features:
Initial light transmittance reaches 90%, but drops sharply to below 70% after aging (UV radiation is a major culprit).
Poor heat retention (temperature difference between inside and outside the greenhouse at night <3℃), requiring heating equipment in winter.
Prone to condensation (dripping water), inducing leaf diseases.
*Suitable Crops:
Short-term fast-growing leafy vegetables (spinach, bok choy)
Seasonal needs such as rice seedling cultivation
2. Polyvinyl Chloride (PVC) Film
*Features:
Strongest nighttime heat retention (2-3℃ higher than PE film), suitable for cold-sensitive crops.
High density (1.3g/cm³), requiring reinforced frame support.
Contains chlorine, incineration will produce dioxins.
*Suitable Crops: Overwintering cucumbers, bell peppers, and other fruits and vegetables. Early spring seedling cultivation in Northeast China.
3. Ethylene-vinyl acetate (EVA) Film
*Features:
A hexagonal warrior balancing light transmittance (92%), heat retention, and lifespan (3-5 years).
Low temperature resistance (not brittle at -30℃), making it the first choice for high-altitude and cold regions.
Good compatibility with anti-drip agents, with an anti-fogging cycle of up to 2 years.
*Suitable Crops: Year-round tomato cultivation in North China. Highland flower cultivation.
4. Polyolefin (PO) Film
*Features:
Utilizes five-layer co-extrusion technology, sandwiching different functional materials.
Dust-proof coating (electrostatic dust repellency) maintains light transmittance attenuation of <5%/year.
Optional infrared blocking layer (heat retention) or quantum dot modulation layer.
*Suitable Crops:
Strawberry elevated cultivation (requires enhanced red light)
Export-grade Phalaenopsis orchid flowering induction
Multi-span greenhouse
II. Classification of Functional Films:
1. Heat-insulating film
* Core technology: Added ceramic microparticles to reflect long-wave infrared radiation.
* Suitable Crops:
Overwintering solanaceous vegetables (night temperature requirement > 10℃)
Off-season dragon fruit (protection against frost damage)
2. Diffuse film
* Core technology: Decomposes direct light into diffused light through a microprism structure.
* Suitable Crops:
Dense canopy tomatoes/cucumbers (improves light penetration to the lower and middle parts)
Delicate flowers (prevents scorching of gerberas)
3. Light Quality Modulating Film
*Core Technologies:
UV Barrier Type: Reduces strawberry powdery mildew incidence by 40%
Blue Light Enhancement Type: Increases lettuce vitamin C content by 25%
*Suitable Crops:
Medicinal Plants (Perilla, Mint) - Accumulation of Secondary Metabolites
Tissue Culture Seedling Acclimatization Transition Period
Multi-span Greenhouses
III. Film Selection Methods
*Climate Differences:
Arid Regions: PO Dustproof Film + Side Shading Net
Humid Regions: EVA Drip-Reducing Film + Top Diffusion Layer
*Crop Differences:
Fruit Types: Prioritize Red Fruits Light transmittance (>85%)
Leafy vegetables: Focus on uniformity (scattered light ratio >50%)
*Cost difference (average annual cost):
Ordinary PE film: Average annual cost 12-15 RMB/㎡ (replaces every 2 years)
Top-grade PO film: Average annual cost 8-10 RMB/㎡ (10-year lifespan)
Note: Modern multi-span greenhouses commonly use a combination of "main film + functional side film," such as a PO high-scattering top film combined with an EVA UV-blocking side-opening film to achieve coordinated control of light, temperature, and humidity. Specific selection needs to be dynamically optimized based on the operating parameters of the fan and water curtain system (such as the impact of humidity on film dripping properties).