Film or polycarbonate is the first real decision of any from-scratch build: skin the structure in 6-mil greenhouse poly for the lowest cost per square foot in horticulture, or invest in rigid multiwall panels that will still be on the roof when the third film cover would have been due. This is the initial-build version of the question — for swapping coverings on an existing structure, see our re-covering guide and replacement panel roundup.
The Contenders
6-mil UV-stabilized polyethylene film is the hoop-house standard: typically 4-year warranted (often serving 5–6), tensioned drum-tight with wiggle wire into lock channel, available in IR/thermal, anti-condensate and diffused grades, and cheap enough to cover a 20x40 tunnel for the price of panelling a garden shed. Twin-wall and multiwall polycarbonate (4mm through 16mm) is the rigid-kit standard: 10–15+ year service life, insulation that roughly doubles film per layer and climbs with thickness, 200-times-glass impact resistance, installed as panels on an engineered frame per our glazing deep-dive.
| Factor | 6-mil greenhouse film | Multiwall polycarbonate |
|---|---|---|
| Upfront cost / sq ft | Lowest in horticulture | Several times film |
| Service life | 4–6 years per skin | 10–15+ years per panel set |
| Insulation | Low; double-layer inflated ≈ twin-wall territory | Strong; rises with 6/8/10/16mm grades |
| Light | High, diffusable grades available | ~80% twin-wall, well diffused |
| Structure required | Hoops + lock channel; light framing | Engineered frame, purlins, precise base |
| Wind behavior | Bulletproof when taut; sacrificial in extremes | Excellent if braced; panels pop from racking frames |
| Snow behavior | Sheds on gothic arches; needs management | Stiffens roof; thickness adds capacity |
| Labor cycle | Re-skin every ~5 years (a helper-day) | Wash annually; replace panels rarely |
The Lifespan Math That Actually Decides It
Run the covering cost over fifteen years. Film re-skinned three times still usually totals less than paneling the same area in 8mm polycarbonate — at tunnel scale, where the areas are huge and the frame is cheap hoops. Shrink to hobby scale (a 6x8 or 8x12) and the math flips: the polycarbonate premium over a small area is modest, while the value of never re-skinning, of insulation that halves the heating bill, and of a structure that reads as a permanent garden building dominates. This is why the market split the way it did: film owns the field, polycarbonate owns the backyard.
The Heating-Bill Tiebreaker
If you heat, insulation is the whole conversation. Single-layer film sheds heat fast enough that winter heating under it is largely a money bonfire; the tunnel world's answer — a double film layer with a small inflation blower — creates an air-gap blanket that lands in twin-wall territory and stiffens the skin against flutter as a bonus. Polycarbonate starts at that level and climbs: 8–16mm grades make modest heaters and the controllers from our thermostat guide genuinely sufficient for year-round growing. Unheated season-extension growers can ignore this section; heated growers should read nothing else.
Light Quality: The Overlooked Variable
Both coverings transmit ample light for growing, but they deliver it differently, and canopies notice. Fresh clear film transmits generously and its diffused grades scatter light deep into dense plantings — one reason production tunnels favor diffusion for uniform ripening. Twin-wall polycarbonate diffuses inherently: the fluted structure turns direct beams into soft, even illumination that nearly eliminates leaf scorch and in-canopy shadows, at the cost of a somewhat lower headline transmission number. In practice the diffusion effect means measured growth under quality multiwall routinely matches clearer coverings — so don't let a few percentage points of transmission spec decide a fifteen-year covering choice that insulation and lifespan should decide.
Failure Modes and Honest Risks
Film's enemies are UV time, flutter from loose tensioning, and contact with PVC or raw pressure-treated lumber (both age it chemically — tape or paint the contact points). Its virtue in catastrophe is being sacrificial: ahead of a hurricane, stripping the skin saves the frame for the cost of a re-skin, per the survivability pillar. Polycarbonate's enemies are racking frames that pop panels (bracing and clips solve it), UV haze in cheap uncoated sheet (buy warranted, coated-face-out panels), and open flutes wicking moisture and algae (tape them at install). Neither material fails on its own schedule when the structure under it is square, braced, and anchored.
Price both skins for your build
Spec your structure's covered area, then price a 4-year 6-mil film roll with wiggle wire against 8mm twin-wall panel packs for the same coverage — the fifteen-year math above turns concrete in about ten minutes of comparison.
Our Verdict
Film for area: tunnels, market beds, and any build where protected square footage per dollar is the mission — double-layer it if you heat. Polycarbonate for permanence: hobby-scale structures, heated winter growing, and buildings meant to look like buildings. The crossover point is roughly where your greenhouse stops being farmland and starts being architecture — and at that point, the panels pay for themselves in heat retained and weekends not spent re-skinning.
Frequently Asked Questions
Is polycarbonate better than plastic film for a greenhouse?
For small, permanent, or heated structures, usually yes — panels last 10–15+ years and insulate far better. For large areas and production tunnels, 6-mil film's cost per square foot is unbeatable even counting re-skins every four to six years.
How long does greenhouse plastic film last?
Quality 6-mil UV-stabilized film is typically warrantied four years and commonly serves five or six when tensioned drum-tight and kept off PVC and raw treated lumber. Non-greenhouse plastic fails within a season.
Does double-layer film insulate like polycarbonate?
An inflated double layer of film creates an air-gap blanket that approaches twin-wall polycarbonate territory while also stiffening the skin against wind flutter — the standard cold-climate upgrade for heated tunnels.
What makes polycarbonate panels fail early?
Racking frames that pop panels loose, cheap uncoated sheet hazing under UV, and untaped flutes collecting moisture and algae. Braced, anchored frames, warranted coated panels installed coated-face-out, and proper flute tape prevent all three.