Choosing corrugated plastic sheet by thickness alone is a common and costly mistake. Two 4mm sheets can feel completely different if their grammage (weight per square metre) differs, and a sheet installed with the wrong flute direction may not carry the load it was bought for. The right balance of strength and cost only appears when you specify four things together: thickness, grammage, flute direction and functional grade.
In this guide, Polariod Enterprise, a Taiwanese manufacturer that extrudes PP corrugated board in its own factory, explains how buyers and engineers can specify the sheet correctly. In Japan this material is widely known as pladan (プラダン), so the guide is also useful if you are sourcing for Japanese customers.
What Is Pladan, and Is It Different from Coroplast or Correx?
Pladan is polypropylene (PP) resin extruded into a twin-wall hollow sheet. It goes by many names: corrugated plastic, PP hollow sheet, fluted polypropylene, and trade names such as Coroplast or Correx in English-speaking markets. In Japan it is called pladan, danpura or purabeniya. These names describe the same basic material; the differences come from regional habits and brand names, not from performance classes.
PP has a specific gravity of about 0.9, making it one of the lightest plastics. Two flat liners joined by vertical ribs create a hollow structure that combines low weight with good stiffness. Compared with paper corrugated board, the key advantages are that it keeps its strength when wet, resists oils and many chemicals, and can be reused many times.
Typical applications include floor and wall protection on construction sites, returnable boxes and dividers in logistics, signage, ESD packaging for electronics and agricultural supplies. Each one calls for a different specification. See our PP corrugated board and hollow profile sheet page for the full range.
Why Is Thickness Alone Not Enough?
Thickness only describes the outer dimension of the sheet; grammage and flute direction determine how strong it is. If a purchase order simply says "4mm," different suppliers may deliver sheets that vary widely in stiffness and weight, which makes price comparison meaningless.
What Is Grammage (g/m²), and Why Does It Change Stiffness?
Grammage is the weight of one square metre of sheet, known in Japan as metsuke (目付). At the same thickness, higher grammage means more resin, thicker liners and ribs, and a stiffer sheet that resists crushing.
At Polariod, for example, 3mm sheet ranges from roughly 400 to 600 g/m² and 4mm from roughly 500 to 800 g/m². On a standard 910 × 1820 mm sheet (about 1.656 m²), 600 g/m² works out to about 1.0 kg per sheet, while 800 g/m² is about 1.3 kg.
Higher grammage adds strength but also adds material cost and weight. The basic rule for cost control is to choose the lowest grammage that still meets your strength requirement. Always compare quotations on a "thickness × grammage" basis.
How Does Flute Direction Affect Bending Strength?
Flute direction is the direction in which the internal ribs run, which is also the extrusion direction. The sheet is stiffer when bending along the flutes than across them. This anisotropy matters in design:
- For shelves and base boards that carry loads, orient the flutes so they span between the supports
- Fold lines parallel to the flutes fold cleanly, often without scoring
- Fold lines across the flutes should be scored first to prevent cracking or rippling
Stating "flute direction: long side" on drawings and purchase orders prevents many problems during converting and box making.
Where Should You Start? 2.5mm and 4mm as Core Specifications
If you are unsure, start your evaluation with 2.5mm and 4mm sheets in the 910 × 1820 mm (3 × 6 ft) format. These are Polariod's main export specifications, which means high production volumes, stable supply and easy planning by pallet or full container.
- 2.5mm: for applications where light weight and easy handling matter, such as wall protection, dividers, light boxes and printed sign substrates
- 4mm: for applications where stiffness and durability matter, such as floor protection, returnable box bodies and reusable dividers and trays
If 2.5mm is not quite strong enough, consider raising its grammage before moving up to 4mm. If 4mm is more than you need, lowering its grammage reduces both weight and cost.
Which Thickness and Grammage Suit Each Application?
The table below is a starting point for specification. Final choices depend on load, number of reuse cycles and environment (indoor or outdoor, humidity, temperature), so we recommend confirming with samples.
| Application | Suggested thickness | Grammage approach | Suggested grade / spec |
| Wall and door protection | 2.5mm | Standard to low (weight first) | Standard; coloured for visible scratches |
| Floor and walkway protection | 4mm | Standard to high (puncture and trolley resistance) | Standard |
| Dividers and inner fittings | 2.5–4mm | Based on product weight | Standard / anti-static |
| Returnable and foldable boxes | 4–5mm | High (repeated use, stacking) | Standard / anti-static / conductive |
| Outdoor and election signs | 2.5–4mm | Standard (wind load vs. weight) | Corona treated, UV stabilised |
| Electronic component trays | 2.5–4mm | Based on component weight | Anti-static (10⁶–10⁹ Ω) / conductive (below 10⁶ Ω) |
| Shelving and large cases | 6–10mm | High (to limit sagging) | Standard |
Send us your thickness and application, and we will recommend specific grammage values.
How Should You Choose Surface Treatment and Functional Grades?
Functional grades should be chosen from the risks of the use environment, not added "just in case." Unneeded functions raise cost, while missing ones can cause defects or incidents.
- Corona treatment: PP naturally resists inks and adhesives. Corona treatment modifies the surface to improve adhesion for screen printing, UV printing and lamination. Treat it as essential if you print or bond the sheet.
- Anti-static grade: surface resistance of 10⁶–10⁹ Ω, which reduces dust attraction and static build-up in packaging for electronic and precision parts.
- Conductive grade: surface resistance below 10⁶ Ω, for applications that need static to be drained quickly.
- UV-stabilised grade: for signs and materials used outdoors for long periods. Tell us how long the installation needs to last.
- Flame-retardant grade: formulated with flame-retardant additives. If the product is going to Japan, note that UL94, the Fire Service Act's bōen (flame-proof) label and the Building Standards Act's fire-performance ratings are separate systems. Confirm which proof your customer needs first.
Learn more on our logistics and industrial applications page and our fire-retardant building materials page.
What Sizes and Converting Methods Are Available?
The standard size is 910 × 1820 mm (3 × 6 ft), which matches the dimensional system used in Japanese construction, site protection and signage. Other sizes and cut-to-size orders can be discussed.
Converting flexibility is one of the material's biggest strengths. Polariod's sheet is well suited to conventional paperboard converting machinery and supports:
- Scoring, cutting, slitting, flat pressing and stitching
- Die-cutting into boxes and trays
- Ultrasonic welding, riveting and laminating
Because existing paperboard equipment can be used, many converters buy our sheet and make boxes locally, which keeps the supply chain simple.
Seven Things to Confirm Before You Request a Quote
Preparing the following seven points makes quotations easier to compare and avoids rework.
- Describe the application: what it is for, how many cycles, and where it will be used (indoor, outdoor, cold storage)
- Choose a thickness: start from 2.5mm or 4mm
- Specify grammage: compare on a thickness × grammage basis
- Specify flute direction: long side or short side
- Select functional grades: corona treatment, anti-static, conductive, UV, flame retardant
- Confirm size, colour and quantity: 910 × 1820 mm or custom size, colour, annual volume
- Validate with samples: test with real loads, converting and printing before mass production
Polariod: A Taiwanese Pladan Factory Built for Export Supply
Polariod Enterprise Co., Ltd. was founded in 2006 and operates its own factory in Dadu District, Taichung, Taiwan. It is a subsidiary of Yi-Sheng Industrial Co., Ltd., a Taiwanese plastics manufacturer founded in 1979. Multiple extrusion lines produce PP corrugated board from 1.5mm to 10mm thick, including volumes for export.
To help overseas customers plan purchases accurately, we publish clear shipping units for our core specifications:
| Thickness | Size | Sheets per pallet | Sheets per 40HQ container | Area per container (calculated) |
| 2.5mm | 910 × 1820 mm | 940 | 14,000 | approx. 23,190 m² |
| 4mm | 910 × 1820 mm | 600 | 8,870 | approx. 14,690 m² |
From your annual usage you can work out the number of pallets and containers, which also helps with inventory and warehouse planning.
Frequently Asked Questions
What is the difference between 3mm and 5mm corrugated plastic?
The main differences are stiffness and weight. The taller hollow section of 5mm sheet resists bending better, so it suits returnable boxes and stacked applications. 3mm sheet is lighter and easier to convert, so it suits dividers, light boxes and protection boards. Because grammage also changes stiffness, always compare thickness and grammage together.
How much does grammage vary from sheet to sheet?
Tolerances depend on the manufacturer and product. The most reliable approach is to agree a nominal grammage and acceptable range when ordering, then weigh sheets at incoming inspection. Polariod can discuss grammage specifications to match your requirements.
Can corrugated plastic be used outdoors?
Yes. PP does not absorb water, so it keeps its strength in the rain. For long-term outdoor use, choose a UV-stabilised grade to slow sunlight degradation. Service life depends on the installation environment, so tell us the expected duration and we will advise.
What colours are available?
White, black, blue, red, green, yellow, translucent and more. For site protection, choose colours that hide dirt; for returnable boxes, colour-code by process or customer to make handling more intuitive.
Which way should I cut or fold the sheet?
Folds parallel to the flutes can usually be made cleanly without scoring. Folds across the flutes should be scored first to prevent cracking or rippling. Small quantities can be cut with a utility knife; for production, cutting machines or die-cutting keep dimensions consistent.
Can I order small quantities from an overseas factory?
It depends on quantity and specification. Polariod offers its core 2.5mm and 4mm sheets (910 × 1820 mm) in pallet and 40HQ container units. Tell us your required quantity and application, and we will suggest the best ordering unit.
Tell Us the Application, and We Will Recommend the Right Thickness and Grammage
The key to choosing corrugated plastic is not picking a thickness from a catalogue but working backwards from the application. As a Taiwanese pladan factory, Polariod combines thickness, grammage, flute direction and functional grade to recommend the right specification and shipping unit for you.
Whether your current sheet is too heavy, or you need to prepare pladan specifications for a Japanese customer, we are happy to help. Send us your application, number of cycles, size and annual volume, and we will arrange samples and a quotation.
- Contact form: Contact us
- Email: po.lariod@msa.hinet.net
Related reading: Durable like plastic, lightweight like paper. PP Corrugated Sheets | Using Corrugated Boxes Three Times and Throwing Them Away?