Two products, one specification language
A greenhouse cover and a mulch film are both polyethylene sheet, and they are bought on completely different numbers. The cover is judged by how much light and heat it holds for three to five seasons. The mulch film is judged by whether it still suppresses weeds in month four and whether it can be lifted out of the field without shredding.
Buyers who send one enquiry for "agricultural film" get quoted two products that cannot be compared. The specification has to be split before the RFQ goes out.
Greenhouse film: what is actually being specified
| Parameter | Typical range | What it decides |
|---|---|---|
| Thickness | 80–200 µm (150 µm common for multi-season) | Tear resistance and how the sheet behaves in wind |
| Width | 4–12 m, wider on request | Number of roof panels and seam count |
| Resin | LLDPE base, LDPE for stiffness, EVA for heat | Thermal retention and flexibility at low temperature |
| UV package | HALS + UV absorber, rated 3–5 seasons | Whether the sheet survives season three |
| Anti-drip (anti-fog) | Surface additive, 4–6 month activity | Light transmission after condensation forms |
| IR additive | 3–8 % of a mineral IR masterbatch | Night-time heat retention |
| Haze | 10–30 % diffusing grades | Scatter versus direct light on the crop |
| Light transmission | 85–90 % new, clear grade | PAR available to the canopy |
The number that gets argued about is thickness, and it is the least useful one on its own. A 150 µm sheet with a weak UV package fails before a 120 µm sheet with a proper HALS loading, because failure in the field is almost always photo-oxidation at a stress point rather than uniform wear.
Seam count matters more than width. Wide rolls reduce the number of overlaps, and every overlap is a place where wind gets under the sheet. A 12 m roll that replaces three 4 m panels removes two seams — worth more than an extra 20 µm of thickness.
Resin choice: why EVA appears in thermal grades
Three-layer co-extrusion is the normal construction above a certain price point. The outer layers carry the UV package and the mechanical strength; the middle layer carries the functional additive.
| Construction | Behaviour | Where it is used |
|---|---|---|
| Monolayer LLDPE | Cheapest, good toughness | Short-season tunnels, single crop |
| LLDPE / EVA / LLDPE | Better heat retention, softer hand | Multi-span greenhouses in cool climates |
| LLDPE / EVA + IR / LLDPE | Heat retention plus fog control | High-value crops, cold nights |
| Metallocene LLDPE skin | Higher dart impact at same gauge | Wind-exposed sites, large spans |
EVA raises the film's infrared absorption and lowers its stiffness. The trade is real: a high-VA middle layer holds heat better and drapes more easily over a frame, but it also blocks less of the sheet from stretching under load. The VA content and layer ratio are the two figures to ask for, not just "EVA film".
Mulch film: a different specification entirely
Mulch film is thin — 8 to 30 µm — and it is laid by machine at speed, so the failure modes are mechanical.
| Grade | Thickness | Colour | Function |
|---|---|---|---|
| Black | 10–20 µm | Black | Weed suppression, soil warming |
| Black-silver | 15–25 µm | Silver face, black back | Weed control plus light reflection for fruit colour |
| Clear | 8–15 µm | Transparent | Early soil warming, no weed control |
| White-black | 20–30 µm | White face, black back | Cooling in hot climates |
| Photodegradable | 12–20 µm | Any | Breaks down in field, avoids removal labour |
Two specifications decide whether the roll survives the laying machine: dart impact and tear resistance in the machine direction. A roll that tears at the roll end costs a field crew an hour, which is more than the film costs.
For degradable grades, the induction period has to be written as a number. "Photodegradable" alone allows a film that embrittles in six weeks or one that is still intact after two seasons; the useful specification is a tensile retention target at a stated UV dose.
Test methods to put in the purchase order
| Property | Method | Note |
|---|---|---|
| Tensile strength and elongation | ASTM D882 | Report MD and TD separately |
| Dart impact | ASTM D1709, method A or B | Method A for thin mulch film |
| Tear resistance | ASTM D1004 | Elongation tear, not trouser tear |
| Haze and clarity | ASTM D1003 | Relevant to diffusing greenhouse grades |
| Light transmission | ASTM D1003 or spectrophotometer | State the wavelength range |
| Accelerated UV ageing | ISO 4892-3, UVA-340 | Report hours to 50 % tensile retention |
| Carbon black content | ASTM D1603 | For black mulch, 1–3 % typical |
| Width and thickness tolerance | Measured at three points across the roll | Ask for the tolerance, not the nominal |
Accelerated ageing hours are not seasons. The conversion depends on the local UV dose, and a supplier who quotes "5 years" without stating the test hours and the reference climate has quoted nothing. Ask for the retention curve, not the endpoint.
What shortens field life
- Sulphur and chlorine in the soil. Fumigation and some fertiliser regimes attack the stabiliser package. Greenhouse film over a fumigated soil needs a different specification from the same film over clean ground.
- Hot spots at the frame. Film in contact with a metal purlin runs hotter, and that is where the first crack appears. Anti-slip or a separated fixing detail is cheaper than a mid-season replacement.
- Edge burying on mulch film. Film buried too shallow lifts in wind; buried too deep it tears at the soil line when lifted.
- Condensation without anti-drip. A sheet that drips loses 10–15 % of its transmission and drips directly onto the crop, which is a disease problem rather than an optical one.
- Storage before use. A roll stored in a hot shed for a season has already started its UV clock. Ask for the production date on the label.
Roll, core and packing
Greenhouse film travels as a folded roll on a 76 mm core, typically 50–100 m per roll, in a woven bag or a carton for export. Two details worth writing down: the fold configuration (how many layers per fold, because that decides how the sheet is unrolled on the frame) and whether the roll is edge-trimmed. An untrimmed roll has a wavy edge that makes seaming slower.
Mulch film runs longer — 500 to 1500 m per roll — and the core has to be strong enough for the laying machine's mandrel.
RFQ checklist
- Product: greenhouse cover, tunnel film, or mulch film, stated separately.
- Thickness and width with tolerances, and total length per roll.
- Construction: monolayer or three-layer, with layer ratio if co-extruded.
- Resin: LLDPE grade, EVA VA content if used, metallocene if specified.
- UV package: HALS type, absorber, target season life with the accelerated ageing hours behind it.
- Functional additives: anti-drip, anti-fog, IR, diffusing; expected activity period.
- Colour and opacity for mulch grades, plus carbon black content.
- Test reports: ASTM D882 MD/TD, D1709, D1004, ISO 4892-3 curve.
- Fold configuration, core diameter, roll weight, packing method.
- Production date on the label and shelf-life statement.
An agricultural film enquiry that states thickness, width, target season life and the test method behind that life will get comparable quotes. One that states "good quality greenhouse film" will get a price and a sample, and the difference shows up in season three.
Related product categories
The materials and part types discussed above are grouped in our sourcing directory:
