CPP and BOPP are the same polymer taken down two different film lines: CPP is cast polypropylene film, quenched on a chill roll and never stretched, and BOPP is biaxially oriented polypropylene film, stretched in both directions after casting. That one step is the whole difference, and the two films do opposite jobs — CPP seals, BOPP carries print and stiffness.
What Is CPP
CPP is cast polypropylene film — polypropylene melt extruded through a flat die onto a chilled roll, edge-trimmed and wound, with no stretching step in the line.
“PP film” on an inquiry is a general term and CPP is one route under it: GCPP, MCPP and RCPP name the general-purpose, metallisable and retort versions. Cast film is specified in tens to low hundreds of microns.
Which resin goes in is settled layer by layer, and all three PP families have cast-film grades. A general-purpose web runs on homopolymer at around 8 g/10 min melt flow (230 °C / 2.16 kg, ISO 1133), while random copolymer grades buy optics, softness and easier welding. The retort grades sold as RCPP are built on impact copolymers, whatever the name suggests.
The sealing face is a different resin again: a cast structure is coextruded with a terpolymer or high-comonomer random copolymer skin that starts sealing well below the temperature at which the core would soften.
What Is BOPP
BOPP is biaxially oriented polypropylene film — a cast sheet reheated and pulled in the machine direction and then across it, so the chains align both ways. A tenter line takes the two stretches in sequence and is the common industrial route; the double-bubble route stretches both directions at once and goes mainly into shrink and overwrap film.
The core has to stay stretchable, so it is a polypropylene homopolymer at around 3 g/10 min melt flow (230 °C / 2.16 kg, ISO 1133), lower flow than the general-purpose cast grades. Sealing comes from a separate layer: a coextruded terpolymer or copolymer skin on one or both faces, or a coating.
The grade families are surface variations on that one process: plain, heat-sealable, matte, pearlised, metallised, label and tape films. Quotations and datasheets often write OPP for the same film.
The Difference Between CPP and BOPP
The difference is orientation, and every property below follows from it. Cast film stays soft and heavy-gauge, which suits it to the sealing face. Oriented film comes out thin, stiff and clear, and carries the print and the strength.
Heat Sealing
CPP’s advantage in sealing is strength, and it is large. At 25 µm, one producer’s sealable CPP carries a minimum seal strength of 1,800 g/25 mm against 375 g/25 mm for its heat-sealable BOPP — same lab, same internal method, same gauge.
Seal temperature does not divide the two the way the trade usually tells it. On those same sheets the BOPP seal skin starts sealing at 105 °C and the standard CPP at 118 °C. Retort CPP seals only from 150 °C.
Stiffness, Clarity and Moisture Barrier
At equal gauge the oriented film leads on stiffness, clarity and moisture barrier, and the cast film leads on stretch. The figures below are one producer’s heat-sealable grades, both measured in one lab at 25 µm.
| Property (method, condition) | BOPP, 25 µm | CPP, 25 µm |
|---|---|---|
| Tensile strength at break, MD / TD (ASTM D882) | 1,200 / 2,500 kg/cm² | 500 / 210 kg/cm² |
| Elongation at break, MD / TD (ASTM D882) | 200 % / 60 % | 450 % / 600 % |
| Haze (ASTM D1003) | 2.7 % | 3.3 % |
| Gloss at 45° (ASTM D2457) | 85 units | 80 units |
| WVTR (ASTM F1249, 38 °C, 90 % RH) | 6.0 g/m²/day | 12 g/m²/day |
| OTR (ASTM D3985, 23 °C, 0 % RH) | 1,700 cc/m²/day | 3,650 cc/m²/day |
Stiffness separates them further than strength does: on one converter’s sheets the oriented film reads about twice the secant modulus of cast film in the machine direction and about four times across it, per ASTM D882. The cast film’s elongation at break is what the trade loosely calls its tear and puncture resistance.
The familiar claim that CPP is the better moisture barrier because it runs thicker does not hold. The thickest CPP on that sheet, 80 µm, still transmits 7 g/m²/day against 6.0 for BOPP at 25 µm; a cast sealant layer adds barrier in proportion to its gauge and nothing more. Neither film is an oxygen barrier — a metallised or EVOH layer provides that.
Both films arrive corona-treated to 38 dyne/cm, and the treatment decays on the roll.
How To Choose The Right One
In most flexible packaging you do not choose one — you specify both. BOPP is the outer web that carries print, gloss and stiffness and CPP the inner sealant: BOPP/CPP for dry goods, BOPP/VMCPP where the pack needs a light and oxygen barrier, PET/RCPP for retort. The sealant grade is then a question of the line and the product — jaw temperature and dwell at running speed, and whether the pack is retorted or frozen.
A mono film is right where one of the two duties is absent. BOPP alone goes into tape, labels, overwrap and twist wrap; CPP alone into bread and produce bags, garment bags and direct-print work.
On cost, keep two bases apart. BOPP goes through the extra conversion step, so it costs more per kilogram converted; both films measure 0.91 g/cc, so whatever yield advantage BOPP has comes from running thinner at equal function, not from weighing less.
Recyclability is a property of the finished structure. An all-PP BOPP/CPP laminate sits in the compatible box of both design guides — RecyClass groups oriented and non-oriented PP as one material, APR prefers over 90 % PP by weight — while a PET or foil layer takes it out of both. Metallised film divides them: RecyClass lists metallisation as non-compatible, APR allows it below a surface-area threshold.