BOPP / PET / PE / CPP: 4 Common Films, 3 Scenario Judgments — Transparency / Stiffness / Heat Seal Temperature
💡 💡 At a Glance
Transparency / stiffness / heat seal temperature comparison of BOPP / PET / PE / CPP 4 common films + 3 follow-up questions when printers receive "I want transparent" orders + 3 failure cases from choosing the wrong film.
In March this year, a snack client in Suzhou came to us: "I need a transparent packaging bag where I can see the nuts inside, but it also needs to have stiffness — it can't collapse on the shelf. Pick a film for me."
I asked him: "What's the bag format? Stand-up pouch or three-side seal? How much weight of nuts will it hold? What sealing temperature is required? Any barrier requirements?"
He didn't know any of it. He just kept insisting: "I want to see inside."
Over 8 years working in printer design, this is the most common and most headache-inducing type of "one-line customer requirement" I've seen.
The Essential Differences Among the 4 Common Films
The 4 most commonly used films in the packaging industry — BOPP, PET, PE, CPP — each have their own unique physical properties. Listing the properties of these 4 films in a table lets printers select correctly by following the chart when customer orders come in.
Type 1: BOPP (Biaxially Oriented Polypropylene)
Transparency: ⭐⭐⭐⭐⭐ (highest transparency among packaging films).
Stiffness: ⭐⭐⭐⭐⭐ (highest stiffness among films).
Heat seal temperature: Relatively high (165-175℃), requires dedicated heat seal equipment.
Common uses: Outer layer of food packaging (laminated with PE/CPP), label film, tape substrate.
Cost: Medium (12-15 RMB/kg, East China 2024).
Type 2: PET (Polyester Film)
Transparency: ⭐⭐⭐⭐⭐ (highest transparency).
Stiffness: ⭐⭐⭐⭐⭐ (highest stiffness).
Heat seal temperature: Extremely high (230-260℃), cannot be directly sealed by standard heat seal equipment; requires lamination with other films or a heat seal coating.
Common uses: High-temperature retort packaging, coffee packaging, vacuum metallized substrate, outer layer of cosmetic tubes.
Cost: Relatively high (18-25 RMB/kg).
Type 3: PE (Polyethylene Film)
Transparency: ⭐⭐⭐ (moderate transparency, slight haze).
Stiffness: ⭐⭐ (poor stiffness, soft texture).
Heat seal temperature: Low (120-140℃), easy to seal.
Common uses: Inner layer of food packaging (heat seal layer), frozen packaging, cling film, heavy-duty bags.
Cost: Low (9-12 RMB/kg).
Type 4: CPP (Cast Polypropylene)
Transparency: ⭐⭐⭐⭐ (good transparency).
Stiffness: ⭐⭐⭐ (moderate stiffness).
Heat seal temperature: Low (130-150℃), good heat seal performance.
Common uses: Inner layer of food packaging (laminated with BOPP), candy packaging, bakery packaging.
Cost: Medium (13-16 RMB/kg).
3 Follow-up Questions When the Customer Says "I Want Transparent"
When customers say "I want transparent packaging," printers should not directly choose BOPP or PET. Ask 3 questions first:
Question 1: "What sealing temperature does your product need?" This question determines the film's "heat seal performance." If the customer uses a high-speed automatic packaging machine (seal temperature 130-150℃), PE or CPP is suitable; if the customer uses manual sealing or a low-temperature sealing machine (120-130℃), only PE can be used.
Question 2: "What barrier properties does your product need?" Barrier properties refer to "the ability to block oxygen, water vapor, and light." If the product is oxygen-sensitive (such as nuts, coffee, milk powder), a high-barrier film is needed (PET, metallized PET, EVOH co-extruded film); if the product is water vapor-sensitive (such as biscuits, chips), a medium-barrier film is needed (CPP, PE).
Question 3: "What is your bag format?" Stand-up pouches, three-side seals, four-side seals, and eight-side seals have different requirements for film "stiffness." Stand-up pouches require films with sufficient stiffness (BOPP/PET + CPP/PE lamination recommended); three-side seals have lower stiffness requirements (single-layer PE or CPP is sufficient).
4 Real Orders Received by Printers for "Transparent Packaging"
Order 1: Customer is making a "nut snack" stand-up pouch and requires visibility of the nuts inside. Needs "high transparency + high stiffness + medium barrier." Recommended solution: BOPP 25μm (outer layer) + CPP 30μm (inner layer) lamination, or BOPP 25μm (outer layer) + PE 30μm (inner layer) lamination. BOPP provides stiffness and transparency, while CPP/PE provides heat seal performance.
Order 2: Customer is making a "coffee bean" vacuum bag and needs visibility of the beans inside, plus high barrier (to prevent coffee bean oxidation). Recommended solution: PET 12μm (outer layer) + AL 7μm (middle aluminum foil) + CPP 30μm (inner layer) lamination. PET provides stiffness and transparency, aluminum foil provides high barrier, and CPP provides heat sealing.
Order 3: Customer is making a "candy" pillow pouch and requires visibility of the candies, with a low machine sealing temperature (130℃). Recommended solution: CPP 25μm single-layer film. CPP has good transparency and a low heat seal temperature, suitable for high-speed candy packaging machines.
Order 4: Customer is making a "frozen food" three-side seal bag, requiring resistance to -18℃ low temperatures and visibility of the dumplings/tangyuan inside. Recommended solution: PE 50μm single-layer (freezer-resistant) or BOPP 20μm + PE 40μm lamination (improved stiffness). PE has moderate transparency but good freezer resistance.
3 Failure Cases from Choosing the Wrong Film
Failure 1: Customer wanted a "stand-up pouch" and the printer recommended single-layer PE. PE has poor stiffness and won't stand up — the bags toppled over on the shelf. The customer ultimately returned 30%, a loss of 150,000 RMB.
Failure 2: Customer wanted a "candy" pillow pouch and the printer recommended BOPP single-layer. BOPP's heat seal temperature is 165-175℃, but the customer's sealing machine ran at 130℃ and couldn't seal it at all. The customer ultimately returned 100%, a loss of 80,000 RMB.
Failure 3: Customer wanted a "coffee" vacuum bag and the printer recommended BOPP + PE lamination without an aluminum foil layer. BOPP and PE have poor barrier properties, and the coffee beans began oxidizing after 2 weeks. The customer complained to the supermarket, which pulled the product from shelves — a loss of 250,000 RMB.
The common lesson from these three failures: choosing the wrong film is not because of "poor film quality," but because of a "mismatch between film selection and product requirements." Printers must clearly understand the customer's product characteristics, machine parameters, and barrier requirements before selecting films.
3-Step Process for Printer Film Selection
Step 1: Confirm bag format. Bag format determines the "stiffness requirement." Stand-up pouches → high stiffness; pillow pouches → medium stiffness; three-side seals → low stiffness.
Step 2: Confirm product characteristics and barrier requirements. Nuts/coffee/milk powder → high barrier; biscuits/chips → medium barrier; candy/frozen food → low barrier.
Step 3: Confirm sealing parameters. Sealing temperature, sealing speed, machine type (automatic/manual). Automatic high-speed machines → medium heat seal temperature; manual low-speed machines → low heat seal temperature.
After confirming the three steps, select films according to an "outer layer + inner layer" lamination solution. The outer layer is typically BOPP or PET (providing stiffness and transparency), while the inner layer is typically CPP or PE (providing heat seal performance). For high barrier requirements, add an AL (aluminum foil) or EVOH layer in the middle.
Film Selection Checklist for Printer Quotes
After the printer's design department receives a customer order, it is recommended to use the following checklist for item-by-item confirmation:
Customer product: _______ (nuts / coffee / candy / frozen food / other)
Bag format: _______ (stand-up pouch / three-side seal / four-side seal / pillow pouch / eight-side seal)
Sealing temperature: _______℃
Sealing speed: _______ bags/min
Barrier requirements: _______ (high / medium / low)
Transparency requirements: _______ (high / medium / low)
Recommended film solution: _______ (outer layer + middle layer + inner layer)
Once the checklist is completed, the printer's design department can quote according to the recommended solution and attach a "film selection rationale" for customer confirmation. This step can prevent over 80% of film selection disputes.
2 Critical Checkpoints for Printer Owners
Checkpoint 1: Customer order confirmation. Customers must fill out the "Film Selection Checklist" when placing orders; orders without it should not be accepted. This is not the printer being difficult — it is the printer being responsible to the customer. Choosing the wrong film results in losses ranging from tens of thousands to hundreds of thousands of RMB, which neither the printer nor the customer can afford.
Checkpoint 2: Sample validation. During sampling, the customer's actual sealing machine must be used to validate sealing temperature, seal strength, and heat seal performance. The customer's sealing machine parameters differ from the printer's — a sample that seals fine at the printer may fail at the customer's site.
The Suzhou nut client was ultimately given a BOPP 25μm + CPP 30μm lamination solution. Samples were validated 3 times using his machine, and each passed before he placed the order. This customer has now placed 6 orders, each ranging from 500,000 to 800,000 pieces.
Further Reading
If the customer is working on "aluminum-plastic composite packaging," the aluminum foil layer thickness selection and barrier performance are detailed in 4 Types of Composite Material Structures in Practice. If the customer has requirements regarding packaging "recyclability," the recyclability differences among BOPP / PE / CPP are detailed in Real Cost Differences Among 4 Types of Packaging Composite Material Structures. If the customer is working on "eco-friendly biodegradable packaging," the comparison between PLA / PBS films and conventional films is detailed in 3 Implementation Boundaries for PLA Coated Paper Cups. If the customer is working on "frozen food packaging," the low-temperature performance comparison of PE / BOPP / PET is detailed in 3 Transition Paths for Plastic Food Bags: QS / SC / SC-GMP.
FAQ
Both BOPP and PET have high transparency — which is the better choice?
It depends on barrier requirements and budget. BOPP has good transparency, lower cost, and a relatively high heat seal temperature; PET has good transparency, better barrier properties (oxygen barrier is 5 times that of BOPP), an extremely high heat seal temperature, and higher cost. If the customer is producing a 'standard food stand-up pouch,' BOPP + CPP lamination is sufficient. If the customer is producing a 'vacuum bag for long-term food storage' (such as coffee, nuts, or milk powder), PET + AL + CPP lamination is more appropriate.
Both PE and CPP can be heat sealed — how to choose?
PE has poor transparency (high haze), poor stiffness, low heat seal temperature (120-140℃), and good freezer resistance. CPP has good transparency, moderate stiffness, slightly higher heat seal temperature (130-150℃), and average freezer resistance. If the customer is producing 'frozen food' or using 'automatic packaging machine sealing,' PE is recommended. If the customer is producing 'candy, bakery packaging' or has 'moderate stiffness requirements,' CPP is recommended.
Customer says 'I just want the cheapest' — how should the printer recommend films?
When customers want the cheapest option, printers should not directly recommend the cheapest film. First clarify the customer's 'minimum performance requirements' — the minimum thresholds for transparency, stiffness, heat seal temperature, and barrier properties. If the customer has no transparency or barrier requirements, single-layer PE can be recommended (cheapest). If the customer requires transparency, stiffness, and heat sealability, the lowest-cost solution is BOPP + PE lamination (22-26 RMB/kg). Printers should not cater to the customer's 'cheapest' demand while ignoring performance thresholds — the losses from failure cases are far greater.
Customer wants 'recyclable film' — which should be chosen?
BOPP, PE, and CPP are all 'recyclable films' (recycling categories 4 / 2 / 5). PET is also a recyclable film (recycling category 1). If the customer wants 'mono-material recyclability,' PE single-layer or BOPP + PE lamination is recommended (both belong to the PE family). If the customer wants 'fully biodegradable,' PLA / PBS / PBAT films are required, but these have weaker heat seal performance and stiffness compared to conventional films and require targeted process adjustments.
Why do some customers use BOPP + PE lamination while others use BOPP + CPP?
BOPP + PE lamination: The PE inner layer provides heat seal performance, while the BOPP outer layer provides stiffness. The advantage is PE's good freezer resistance, making it suitable for frozen food packaging; the disadvantage is PE's poor transparency, so the overall bag transparency is not as good as BOPP + CPP. BOPP + CPP lamination: The CPP inner layer provides heat seal performance, while the BOPP outer layer provides stiffness. The advantage is CPP's good transparency, resulting in higher overall bag transparency; the disadvantage is CPP's average freezer resistance, making it suitable for ambient temperature food packaging. Customers choose based on their product's temperature requirements.
When printers receive a 'food vacuum bag' order, what film solution should they recommend?
The film solution for food vacuum bags depends on product type and shelf life requirements. Short-term storage (1-3 months): PET + PE lamination, or BOPP + PE lamination. Medium-term storage (3-12 months): PET + AL + PE lamination (aluminum foil provides high barrier). Long-term storage (over 1 year): PET + AL + CPP lamination, or multi-layer co-extruded films (such as PA / EVOH / PE). Printers must clarify the customer's shelf life requirements before recommending, otherwise the barrier grade may be chosen incorrectly.
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