The Industrial Logic Behind Pasted Open Mouth Paper Bags

Pasted Open Mouth Paper Bags are a form of multiwall paper sack made with two or more paper plies, normally converted into a tube, closed at one end by the bag manufacturer, and left fully open at the other end for filling. In a pasted open mouth design, the factory end is folded and bonded with adhesive to form a stable bottom, while the customer fills through the wide top opening and then closes that mouth by sewing, hot-melt bonding, pinch sealing, tape, or heat sealing when a sealable inner structure is present. Open mouth sacks may be flat or gusseted, and the wide filling entry works with simple manual stations as well as automated vertical-spout systems.

The word “paper” can make the format sound simple, but a modern sack wall is engineered rather than merely stacked. The outer ply carries graphics, rub, and handling damage. The middle ply or plies spread tensile load and resist puncture growth. The innermost ply faces product dust, abrasion, fat, moisture, or contamination risk. A coating or separate PE Liner can add a barrier that paper alone cannot provide. Every layer has a job. Every job must support the next one.

This is why Pasted Open Mouth Paper Bags should be understood as the open mouth version of multiwall paper packaging, not as a separate material family. Multiwall design gives the converter several control points: paper grade, basis weight, machine-direction and cross-direction strength, stretch, air resistance, ply count, seam overlap, bottom geometry, mouth reinforcement, and barrier placement. Sack kraft paper is produced for high strength and useful porosity, allowing air displaced by powders to leave the package while the fibrous wall holds the product inside. That balance supports faster filling, cleaner bag shape, and better pallet stability.

Compared with a valve sack, an open-mouth sack gives the filling operator a larger and more visible entry, broader product compatibility, and more choice after filling. The trade-off is that the top requires a separate closing operation and careful control of dust, folds, and seal cleanliness. Compared with a thin plastic sack, the multiwall paper body offers greater stiffness and an excellent printing surface, but moisture protection must be designed rather than assumed. The format succeeds because it does not force one answer on every product. It gives the packaging engineer a platform.

Kraft Paper Options and What Each One Changes

Kraft paper begins with chemical pulp whose long fibres are retained to build tensile and tear performance. For industrial sacks, the important question is not simply “white or brown.” The real question is what the selected paper must do: print cleanly, absorb impact, resist a tear, release filling air, tolerate humidity, contact the product, or carry a coating. VIDEPAK therefore treats paper colour, fibre behavior, stretch, surface finish, and barrier treatment as separate specification choices.

White Bleached Kraft Paper is selected when the package must communicate cleanliness, precision, or premium brand value. Its bright surface improves contrast for light colours, half tones, barcodes, safety symbols, and detailed product instructions. The practical benefit is visual control: the print starts from a more neutral base, so colour variation is easier to manage. Yet whiteness is not strength. VIDEPAK specifies White Bleached Kraft Paper by sack-grade performance, basis weight, surface quality, and required print result, rather than treating every white sheet as equal. White sack paper is especially useful as the outer ply, while strong inner brown or extensible plies can carry much of the mechanical load.

Brown Unbleached Kraft Paper keeps the natural kraft colour and is widely chosen for industrial strength, a direct material story, and a practical cost-to-performance balance. The darker surface supports bold line graphics, strong single colours, and a familiar heavy-duty look. It is also versatile: Brown Unbleached Kraft Paper can serve as the visible outer ply, a hidden reinforcing ply, or an inner contact ply when the product and regulatory requirements allow it. For feed, minerals, chemicals, seeds, charcoal, and construction products, the natural appearance often fits the market while the fibre network handles rough logistics.

Extensible Paper changes the discussion from “How thick is the paper?” to “How much energy can the paper absorb before it breaks?” Standard flat sack kraft commonly has lower stretch, while semi-extensible grades may provide roughly 5–7 percent machine-direction stretch and fully extensible grades more than 8 percent. Tensile energy absorption, or TEA, combines tensile strength and stretch; it correlates closely with drop performance because the sack wall must deform and absorb the moving force of the product rather than crack suddenly. High-quality Extensible Paper can therefore support fewer plies or lower basis weight while maintaining a required sack-wall strength, provided the complete bag has been validated.

PE Coated Kraft paper combines a structural paper base with a bonded polyethylene surface. The paper carries load and supports conversion; the PE layer limits water-vapour transfer, liquid contact, grease migration, or dust penetration, and it may provide a heat-sealable face. This integrated structure is thinner and more fixed than a loose film bag, which can improve bag-making consistency. However, PE Coated Kraft paper is not automatically the best barrier for every product. The coating level, side of application, seal method, air-release requirement, food-contact status, and end-of-life route must all be confirmed. Barrier-coated sack paper can protect against moisture without a separate free film, but any barrier changes the relationship between protection and deaeration.

How Ply Count Builds Performance

Common industrial Pasted Open Mouth Paper Bags use two, three, or four paper plies, although special projects may use more or fewer. A ply is one continuous paper wall, not simply a visual layer. Its basis weight is often selected in the general sack-paper range of about 70–90 g/m², but stronger, lighter, heavier, coated, porous, or wet-strength grades may be used. Ply count must never be read as a strength guarantee by itself. Two high-TEA plies can outperform three weak plies; four badly matched plies can fill worse than a well-designed three-ply sack. The engineering target is total wall performance, not a larger number on a data sheet.

Lean Two-Ply Construction

Two-ply Pasted Open Mouth Paper Bags are the leanest mainstream multiwall structure. The outer ply is commonly Brown Unbleached Kraft Paper for a natural industrial face or White Bleached Kraft Paper for higher graphic contrast. It should resist scuffing, carry ink, and survive corner impacts. The inner ply normally adds tensile load, puncture resistance, product compatibility, and controlled porosity. In a high-performance design, one or both plies may be Extensible Paper, allowing the wall to stretch under a drop instead of failing at the first stress peak.

This structure is attractive because it uses less paper, folds more easily, stores compactly, and can release air quickly. It is often considered for lighter or moderate pack weights, short-to-medium logistics, and products that are not highly moisture sensitive. Yet advanced Extensible Paper can make a two-ply sack suitable for demanding loads, including some 50 kg applications, when paper TEA, dimensions, closures, filling conditions, and drop tests support the design. Industry sack-strength guidance shows that two 70 g/m² high-quality plies can reach the same total strength target for which lower-quality paper may require two 90 g/m² plies. Less can be more—but only when measured.

Recommended options include an outer White Bleached Kraft Paper plus inner Extensible Paper for a brand-led bag; two plies of Brown Unbleached Kraft Paper for straightforward dry goods; or an outer structural ply plus inner PE Coated Kraft paper when moderate moisture or grease resistance is needed. The last option requires careful air-release design because the coating can slow deaeration.

Balanced Three-Ply and Barrier Four-Ply Construction

Three-ply Pasted Open Mouth Paper Bags provide a broad design window. The outer ply manages branding and first contact with the supply chain. The middle ply acts as a structural bridge, spreading tensile load around the tube and supporting the pasted bottom. The inner ply faces the product and can be chosen for cleanliness, abrasion resistance, porosity, or barrier performance. This separation of duties is valuable when the product is dense, the pallet route is long, handling is partly manual, or bag failure would create high cleanup and rework costs.

A practical three-ply build might use 80 g/m² White Bleached Kraft Paper outside, 70–80 g/m² Extensible Paper in the middle, and 70–80 g/m² Brown Unbleached Kraft Paper inside. Another project may use brown outer and middle plies with an inner PE Coated Kraft paper. These are starting architectures, not fixed formulas. Product bulk density changes the force on the wall; particle shape changes puncture risk; trapped air changes bag volume; humidity changes paper behavior. VIDEPAK therefore confirms the build through sample conversion and filled-bag testing rather than relying on ply count alone.

Four-ply Pasted Open Mouth Paper Bags with a PE Liner are selected when mechanical risk and barrier risk are both high. The four paper plies form the load-bearing shell; the separate PE Liner forms the internal containment and moisture barrier. A common layer logic is: printable outer ply, high-TEA reinforcing ply, secondary structural ply, clean inner paper ply, then the film liner. The outer may be White Bleached Kraft Paper or Brown Unbleached Kraft Paper. The reinforcing plies often use Extensible Paper or strong unbleached sack kraft. The innermost paper protects the film from conversion stress and helps the paper body keep its form.

The PE Liner may be a loose sleeve or a fitted and pasted inner bag. Typical project thicknesses can fall around 20–80 μm, with about 30–60 μm frequently considered for ordinary industrial moisture and dust control; the final gauge depends on particle sharpness, seal strength, drop conditions, and shelf-life target. The liner can be sealed independently before the paper mouth is sewn or folded, creating two levels of closure: film for containment, paper for carrying strength. This design suits fine chemicals, hygroscopic powders, food ingredients, fertilizer components, and other products where a simple coated ply may not provide enough protection.

Barrier Engineering with Coatings and Liners

Moisture protection is not a switch that is simply turned on. It is a controlled compromise between water-vapour resistance, air escape, seal integrity, material use, and recyclability. Dry powder may arrive at the filling spout carrying a large volume of air. If the bag wall and mouth trap that air, the sack can swell, underfill, deform, or build an unstable pallet. If the wall is too open, humid air can reach a sensitive product during storage. The correct design lets filling air out at the right stage while limiting moisture entry afterward.

PE Coated Kraft paper is bonded and positionally stable. It cannot bunch inside the sack, and a heat-sealable coating can support a neat mouth or inner-ply seal. It also avoids the movement of a loose film during filling. However, a coating covers only the areas where it is applied; folds, pasted joints, cut edges, perforations, and closure details remain part of the barrier system. A strong coating with a weak mouth is still a weak package.

A PE Liner behaves more like a bag inside a bag. It can create a continuous film envelope and can be independently heat sealed, which is valuable for fine powders and moisture-sensitive contents. Loose liners are easier to separate after use but may shift or wrinkle. Pasted liners stay aligned and can run more predictably on some filling systems, but separation can be less convenient. Thick film improves puncture margin, yet also adds material, stiffness, and cost. Thin film saves material, yet demands better handling and smoother product contact. The choice should follow measured risk, not habit.

For recycling, a predominantly paper structure is usually the simplest starting point, while coatings and films require attention to local collection and mill acceptance. A removable PE Liner can allow paper and film to be separated, but only when the bag design and customer handling process make separation practical. Sustainability is therefore not a label attached to one material. It is the result of sufficient protection with no unnecessary layer, reliable product delivery with low breakage, and an end-of-life route that is realistic in the destination market. Paper sacks made from virgin long fibres also contribute useful fibre to recycling streams when correctly collected.

From Product Data to a Finished Bag Specification

A reliable specification begins with the product, not the bag. VIDEPAK reviews bulk density, nominal fill weight, particle size, flowability, abrasiveness, dust level, moisture sensitivity, fat or oil content, odour sensitivity, food-contact needs, filling temperature, and expected shelf life. The team then studies the customer’s line: filling spout size, clamping method, air volume, weighing system, top closure, conveyor speed, metal detection, pallet pattern, and stretch wrapping. Packaging works when product behavior and machine behavior meet in the same design.

Dimensions must be calculated around filled volume, not copied from a previous bag. Width, length, gusset, and bottom depth determine how easily Pasted Open Mouth Paper Bags fit the spout, how completely they fill, and how they settle on the pallet. An undersized bag can trap air, stress the seams, and make the top difficult to close. An oversized bag can wrinkle, fill loosely, and create rounded, unstable pallet layers. Correct geometry is quiet engineering: the customer may not notice it when it works, but everyone notices when it does not.

Closure design is equally specific. A sewn top is flexible and familiar, and paper tape can reinforce the line and support easy opening. A pinch or hot-melt closure gives a cleaner, more continuous seal where sift resistance matters. When PE Coated Kraft paper is used as a sealable inner ply, heat can close the barrier before the outer paper is finished. When a PE Liner is present, the liner can be heat sealed first and the paper mouth sewn or bonded second. Two closures, two functions: containment inside, carrying strength outside.

Testing closes the design loop. Paper properties such as grammage, moisture, tensile strength, stretch, TEA, tear, air resistance, and water absorption provide the material baseline. Finished-bag tests show whether the converting details work together. Drop testing is especially valuable because it exposes weak folds, poor gluing, unbalanced plies, puncture paths, and closure faults under realistic impact. Filling trials reveal air-release behavior and mouth compatibility. Storage trials reveal moisture gain, caking, print rub, and pallet creep. Data should decide the final specification.

Applications, Quality Control, and the VIDEPAK Value

Pasted Open Mouth Paper Bags serve markets where a product must move efficiently from a hopper to a pallet, from a warehouse to a customer, and from sealed protection to easy opening. Food ingredients such as flour, sugar, starch, dairy powders, and dry mixes benefit from clean inner layers, clear printing, and optional barrier control. Animal feed, seed, and agricultural products need puncture resistance, rough-handling strength, and readable instructions. Chemicals, minerals, and fertilizers may demand a PE Liner, strong seam design, hazard communication, and controlled dust. Construction materials need high TEA, air release, and resistance to repeated drops. Open-mouth sacks are widely used for powdered, granular, and loose-fill products across these categories.

The correct paper choice changes with the market message. White Bleached Kraft Paper can help a food ingredient or premium formulation look clean and controlled. Brown Unbleached Kraft Paper can give feed, seed, charcoal, minerals, or building materials a direct and durable identity. Extensible Paper can reduce breakage risk where manual handling and long transport routes create repeated shocks. PE Coated Kraft paper can protect products that need an integrated moisture or grease barrier. A separate PE Liner can support stronger containment where fine particles or humidity create a higher loss risk.

VIDEPAK’s role is to turn these options into one controlled production specification. That includes paper procurement, printing alignment, tube dimensions, ply tension, adhesive placement, pasted-bottom geometry, liner position, mouth finish, stack quality, and batch inspection. The company offers multiwall structures, open-top designs, PE-coated options, loose or pasted liners, flat and gusseted formats, pasted block bottoms, sewn closures, and customized mouth features. Its kraft sack range is designed for industrial products from small packs to heavy-duty formats, with quality systems aligned to established international test methods.

The best Pasted Open Mouth Paper Bags are not the thickest bags, the whitest bags, or the bags with the most layers. They are the bags in which every layer earns its place. White Bleached Kraft Paper earns its place through print and presentation. Brown Unbleached Kraft Paper earns its place through dependable structure and a natural industrial face. Extensible Paper earns its place by absorbing impact. PE Coated Kraft paper earns its place through an integrated barrier. A PE Liner earns its place when the product needs a separate protective envelope.

That is the central value of VIDEPAK’s product approach: not paper for paper’s sake, not plastic for plastic’s sake, not extra plies for comfort’s sake, but a measured architecture for the product and the process. Strong where it must carry. Open where it must fill. Sealed where it must protect. Clear where it must communicate. For customers seeking reliable, printable, and adaptable industrial packaging, VIDEPAK Pasted Open Mouth Paper Bags provide a practical platform that can be engineered from a lean two-ply sack to a robust four-ply structure with a sealed PE Liner—and every carefully chosen option in between.