Professional Manufacturer of Durable Postal Cardboard Boxes

As a professional manufacturer and supplier in China, ZHONGYI specializes in the mass production and customization of postal cardboard boxes across a full range of specifications. Our products cover national standard sizes (Nos. 1–12) and feature various corrugated material grades, box designs, and functional finishes, making them suitable for scenarios ranging from e-commerce fulfillment and personal shipping to sample mailing. We also offer a wide variety of other corrugated cardboard boxes; please feel free to contact us for inquiries.

Which items are suitable for each size/model?

1. Nos. 1–2 (Extra-Large Postal Boxes): High-capacity, sturdy boxes with excellent load-bearing capabilities. Ideal for packing bulky items such as large bedding sets, complete clothing collections, and large quantities of household goods. Commonly used for shipping large e-commerce orders or consolidating multiple small items for whole-home shipments. They offer high stacking stability; using edge protectors and reinforcing pads can effectively prevent box collapse or damage.

2. Nos. 3–4 (General-Purpose Large E-commerce Boxes): Mainstream shipping sizes with balanced dimensions; easy to handle and widely stocked. Suitable for standard goods like apparel, footwear, snack gift boxes, maternity and baby products, and general household items. Available in 3-ply or 5-ply materials; can be paired with paper shred fill or die-cut inserts to secure items and minimize impact damage during transit.

3. Nos. 5–6 (Popular Small-to-Medium Boxes): The most frequently circulated sizes in courier networks. Lightweight, efficient to pack, and space-saving for logistics. Ideal for small items such as beauty and skincare products, books and documents, digital accessories, and small gifts. Standard 3-ply B-flute material is sufficient for daily short-to-medium-distance shipping needs.

4. Nos. 7–12 (Mini/Small Item Boxes): Sizes decrease incrementally, with No. 12 being the industry's smallest standard size. Specifically designed for the precise shipping of items like documents, jewelry, stationery samples, precision components, and laboratory samples. These require no heavy-duty reinforcement accessories; standardized packing can be achieved with simple protective filling.

What is the difference between 3-ply and 5-ply postal boxes? 

The number of corrugated layers, flute type, and material quality are the core factors determining the rigidity, compressive strength, and load-bearing capacity of postal cardboard boxes. They are primarily categorized into two types—three-layer single-wall and five-layer double-wall—to suit various logistics scenarios involving different item weights and shipping distances.

1. Three-layer single-wall postal boxes

Made from standard B-flute cardboard, these boxes feature a smooth surface, excellent printability, easy folding, and lightweight construction, which helps reduce shipping costs for heavy items. They come in three grades: standard, reinforced, and extra-rigid. The standard version is suitable for short-distance shipping of small, lightweight items (under 3kg). The reinforced version offers greater toughness, making it ideal for the daily shipment of standard goods weighing 3–10kg. The extra-rigid version boasts superior crush resistance, making it perfect for bulk packing and short-term warehouse stacking.

2. Five-layer double-wall postal boxes

These utilize a composite BC-flute structure, combining the abrasion and puncture resistance of B-flute with the cushioning and shock-absorbing properties of C-flute. They are thick and rigid, capable of supporting loads of up to approximately 30kg. Highly durable and resistant to crushing or splitting, they are suitable for heavy or fragile items such as small hardware, kitchenware, books, and premium gift boxes. They withstand rigorous conditions like long-distance, cross-province transport and multiple sorting stages; when paired with reinforcement accessories, the risk of damage is significantly reduced.

For which packaging scenarios are full-height and half-height postal boxes suitable?

Based on their height and structural design, postal cardboard boxes are categorized into two main types: standard full-height and half-height (flat) boxes. These precisely meet the distinct packaging needs of three-dimensional versus flat items, effectively solving issues such as shifting, bending, or excessive internal gaps.

1. Standard full-height postal boxes

This is a versatile, standard design with balanced length, width, and height proportions. It offers ample internal space for three-dimensional items and accommodates the vast majority of standard goods. Highly compatible, these boxes work well with automated packaging lines and multi-layer warehouse stacking. They are a popular choice for e-commerce warehouses, courier depots, and individual shipments, and can be used with a wide range of standard packaging accessories. 

2. Low-Profile Flat Postal Boxes

These boxes feature a significantly reduced height and a neat, flat profile. Specifically designed for thin items such as books, art albums, photo frames, tablets, and folded garments, they effectively minimize internal void space—reducing the need for void-fill materials—and prevent items from bending or warping. They stack neatly without tipping over, making them ideal for the standardized shipping of cultural/creative products, printed materials, and flat gifts.

What are the different quality grades?

In accordance with industry production and testing standards, postal boxes are categorized into a three-tier quality system. Key acceptance criteria include flute uniformity, bond strength, bursting strength, moisture content, and resistance to deformation, catering to various procurement budgets and usage scenarios.

1. Basic/General-Purpose Grade: Made from standard 3-ply B-flute material. It offers reliable basic performance and excellent cost-effectiveness; suitable for small, lightweight items and one-time short-distance shipping, meeting the needs of individuals and small businesses for low-cost dispatch.

2. Reinforced/Durable Grade: Features upgraded, high-rigidity base paper with neat fluting and tight bonding (no delamination or flute breakage). It resists crushing and deformation, making it suitable for high-volume e-commerce shipping, inter-city transport, and standard multi-layer stacking. It is the most widely circulated, cost-effective style on the market.

3. Extra-Rigid/Heavy-Duty Grade: Utilizes thickened, extra-rigid 3-ply B-flute or 5-ply BC double-wall corrugated board. With dense paper fibers and superior mechanical properties, it offers high compression, burst, and impact resistance. It is designed to withstand long-distance transport, rough handling during sorting, and heavy stacking loads, making it ideal for the high-standard packaging of valuable, fragile, or heavy items.

How do you choose postal boxes and accessories?

When selecting postal cardboard boxes, follow these core principles: choose 3-ply for lightweight items, 5-ply for heavy items, and low-profile boxes for thin items. For small items and sample documents, bubble wrap or paper shred serves as basic protection; standard goods—such as cosmetics, apparel, and snacks—utilize dividers, inserts, and standard corner protectors to prevent friction and impact damage. Large bedding items and bulk shipments destined for long-distance transport use thickened five-layer cartons paired with reinforced corner protectors and base pads to enhance stacking stability. Flat items like books and photo frames are packed in low-profile cartons with flat dividers to prevent bending. For humid environments or cross-border shipping, waterproof cartons combined with desiccants guard against moisture damage, comprehensively minimizing the rate of logistics-related breakage.

ZHONGYI operates a mature, large-scale production system for postal cartons, covering the full range of national standard sizes (No. 1 through No. 12). We offer customization for three-layer and five-layer boxes, as well as full-height, flat, and specialized functional designs. We maintain strict quality control over flute uniformity, adhesive strength, and structural integrity, supporting rapid delivery for both small and large orders with a comprehensive range of complementary packaging accessories available for one-stop sourcing. We invite logistics and e-commerce enterprises to contact us to discuss partnerships and develop tailored, end-to-end packaging solutions.