Multiwall Kraft Paper Bags Factory: Bottom and Top Options

Multiwall kraft paper bags are heavy-duty, multi-ply containers designed for demanding industrial and consumer packaging. Built from several layers of robust kraft paper (often 2–5 plies) bonded together, these bags combine the strength of paper with versatile sealing options. They can handle coarse grains, powders or chemicals with ease, yet present a clean, printable surface for branding. The “multiwall” structure absorbs impacts and resists tearing, making these bags ideal for high-speed filling lines and long-haul freight. In short, a multiwall paper bag stands up like a box but folds flat for storage – the best of both worlds.

Multiwall bags come in various styles, each defined by its bottom and top construction. Below we introduce the main types: open-top (open-mouth) bags, pinch-bottom open-mouth (PBOM) bags, block-bottom open-mouth (BBOM) bags, gusseted open-mouth (self-opening satchel) bags, sewn open-mouth (SOM) bags, pasted valve (PV) bags, and satchel-bottom open-mouth (Webb pinch) bags. We explain what each style is, how it is built, and what makes it different or advantageous.

Open-Top Multiwall Paper Bags

Open-top (or open-mouth) multiwall paper bags are bags that have a sealed bottom and an open top for filling. They are the simplest form of multiwall sack: the bag is typically formed from a paper tube with one end factory-sealed (often by gluing or folding), while the other end is left open. This open top allows product to be poured or blown in from above. After filling, the open end is closed by the customer using a sewing machine, a heat sealer, or adhesive tape.

Because their bottoms are fully pasted or folded at the factory, open-top bags sit flat on a surface without support. They may be made with flat sides or with side gussets, and in smaller sizes they are often “self-opening” (pre-creased so that they pop into shape when slid onto a hopper). Open-top bags offer economical packaging: with no fill spout or valve built in, they cost less and can be custom-sized for many applications. They excel in applications where speed is moderate and the product is not extremely moisture-sensitive – for example, pet foods, feed, seed, or retail-size flour bags. Their main structural feature is that one end is fully closed (block or folded), while the other end remains open until after filling. Because closure is done manually or by a sewing head, they require more labor than valve or heat-sealed bags, but they are rugged and flexible.

• Structure: Factory-sealed bottom (flat or pinched); top end cut flush.
• Closure: Hand sewing, sewing tape, or heat seal after filling.
• Features: Basic “bag pipe” format; accommodates flat tube or side-gusseted bodies; sturdy support when filled.
• Uses: Animal feeds, grains, horticulture products, cement mixes in retail bags, and other bulk goods where a simple sewn closure is acceptable.

Pinch Bottom Open Mouth (PBOM) Multiwall Paper Bags

Pinch-bottom open-mouth (PBOM) bags are industrial multiwall bags engineered for fast filling and dust-tight closure. In a PBOM bag, the bottom is formed by two triangular “pinch” folds which are fully glued together at the factory, creating a flat, square base. The top of the bag is left open, with a pre-applied hot-melt adhesive or heat-seal tape on the inner top flap. During filling, product is poured in from above; then a pinch sealer (often hot-air or ultrasonic) folds the top ends of the bag and activates the adhesive to weld the flaps shut.

Key characteristics: A PBOM bag stands up on its glued bottom like a block, but its sides slightly taper at the very bottom due to the pinch. Its sealed top closure is virtually airtight and creates a “sift-proof” barrier against dust. This makes PBOM bags ideal for powders and fine materials – flour, cement, sugar, chemicals – that must not leak or spoil. The pinch seal process is rapid, supporting high-speed lines. PBOM bags typically use 3–5 plies of strong unbleached or bleached kraft paper (70–100 g/m² each), laminated with water-based adhesives. Optional inner linings (PE film, EVOH, etc.) or coatings can add moisture or oxygen barrier if needed.

Advantages:
– Leak-proof sealing: The factory-pasted bottom plus the heat-activated pinch top make PBOMs highly dust-tight.
– High fill rates: Wide open top and flat base mean machines can fill and seal thousands of bags per hour.
– Pallet stability: The square bottom and well-creased sides yield flat-faced pallet stacks.
– Versatile: Can carry everything from fine chemicals to food ingredients, with printing and liners.

Despite the complexity of their seal, PBOM bags are easy to operate. After filling, a single fold and a quick heat-seal cycle closes each bag. Compared to sewn bags, PBOMs provide much stronger containment (no needle holes) and better moisture resistance (adhesive forms a near-hermetic seal). Their only drawback is the need for pinch-seal equipment on the filling line, but for many producers this tradeoff is worthwhile.

• Structure: Fully pasted pinch-fold bottom (square when filled); open top with pre-coated adhesive tape.
• Closure: Hot-air or ultrasonic pinch sealer on the top flaps after filling.
• Features: Hermetic seal, tear-resistant multiwall construction, optional liners (PE, foil), printed facings.
• Uses: High-speed filling of cement, flour, chemicals, dry ingredients, pet food, pharmaceuticals, and any dusty or moisture-sensitive bulk powder.

Block Bottom Open Mouth (BBOM) Multiwall Paper Bags

Block-bottom open-mouth (BBOM) bags are multiwall bags with a flat, square base (block bottom) that is fully pasted by the manufacturer. The sides of a BBOM bag are straight (parallel), giving it a rectangular cross-section. The top is open for filling, and after filling the open end is closed manually (by sewing) or by heat seal. In other words, BBOM is simply an open-mouth bag whose bottom layers have been glued all together in a block to form a rigid base.

This block-bottom design provides excellent load-bearing strength. When filled, a BBOM bag can stand unsupported, making it convenient for storage and display. The straight sides (often with optional side gussets) give maximum internal volume with minimal awkward taper. These bags commonly have 2–4 plies of kraft paper in the base (sometimes more for heavier weights), and can be made with barrier layers just like other multiwall styles. Because the bottom is solid, BBOM bags can handle heavy granular loads (pet food, pellets) and withstand stacking pressure.

Differences from PBOM: Unlike PBOM bags, which have pinch-folded corners at the bottom, BBOM bottoms are a simple glued block. BBOM sides are fully vertical, whereas PBOM sides pinch in at the very bottom. On the top end, BBOM bags do not come with adhesive already applied – they usually require sewing or manual heat-sealing to close. Therefore, BBOM bags are slightly simpler to produce but require extra closure steps. They may not be quite as airtight as PBOM unless a liner or heat sealing machine is used.

• Structure: Fully glued square bottom (block); optional side gussets for extra volume.
• Closure: Thread-sewn, heat-sealed or taped shut by the user after filling.
• Features: Excellent stacking strength; rigid, self-supporting base; vertical sides maximize capacity; moisture barrier options available.
• Uses: Dense bulk goods like feed, seeds, specialty grains, fertilizer, and retail products (flour, sugar) where sturdy standing bags are needed but ultra-tight top seal is not essential.

Gusseted Open Mouth (Self-Opening Satchel) Bags

Gusseted open-mouth bags – often called Self-Opening Satchel (SOS) bags – are a special block-bottom style with built-in side gussets. They combine the strong block base of a BBOM with pre-scored creases that allow the bag to open into shape by itself. In manufacturing, the tube of paper is folded so that when the bag is pushed onto a filling machine’s cone, it “pops” open with a square base. The bottom itself is formed by glue, just like a block-bottom bag.

The magic of SOS bags is convenience: they stand up on their own without any support, saving operators the hassle of propping bags open. Because of the gussets, these bags hold more volume for the same outer dimensions, and they maintain a flat-faced stack. Top closure is done after filling, typically by sewing or hot tape. Like other multiwall bags, SOS versions can include barrier liners (PE, foil) and vivid flexographic prints on the outer panels.

Key differences: Compared to a plain BBOM bag, the SOS has gusseted sides and is designed for automatic opening. Compared to PBOM or satchel (Webb) bags, the SOS does not have a pre-applied pinch seal; the top is simply open until the filler closes it. It is best in medium-to-large bag sizes (10–25 kg or more) for products like sugar, flour, petfood, charcoal briquettes – anywhere a retailer-ready bag is desired. The gussets improve cube efficiency on pallets. However, because SOS bags rely on manual or sewing closure, they are less hermetic than hot-sealed bags.

• Structure: Block bottom base with side gussets (satchel style); pre-creased for self-opening.
• Closure: Sewn or taped closed after filling (no factory adhesive).
• Features: Instantly stand-up open mouth; large print surface; stable pallet stacks; easier manual filling.
• Uses: Retail and food products (flour, sugar, snacks, pet food) and general goods where ease of use and appearance matter.

Sewn Open Mouth (SOM) Multiwall Paper Bags

Sewn open-mouth (SOM) bags are the classic multiwall bag style that dates back to the earliest industrial sacks. They are essentially open-top bags factory-closed on one end (either flat or block bottom) and shipped with the other end fully open. After filling on a vertical hopper or conveyor, the user closes the top by stitching through a reinforced seam tape. This thread-stitched closure creates a flush, dirt-tight seal.

SOM bags come in flat tube (no gussets) or gusseted versions and can handle loads from 25 lb (11 kg) up to 50 lb (25 kg) or more. Because no hot-melt adhesive is used, they rely on durable stitching (often with paper thread tape) to stay shut. The bottom of an SOM bag may be either a pasted pinch fold (for smaller bags) or a full block bottom (for larger sizes). Compared to PBOM, SOM bags are more economical (no pre-glue lines), and they need only a sewing machine to seal. However, the needle holes mean they are not completely sift-proof – fine powders can sometimes escape if the seams are not taped over.

Features: Simple design; very robust construction for coarse products; flexible side option (flat or gusset); no factory glue at top. They are well-suited for agricultural products, animal feed, seeds, fertilizers, and building materials like gypsum or salt. Because there is no adhesive, the bags can be opened and reclosed relatively easily by unpicking the stitch (a drawback for tamper-evidence, but an advantage for some uses).

• Structure: Flat or gusseted tube, factory-closed bottom (block or pinch); top flush-cut open.
• Closure: User sews the top with thread (through crepe or paper tape).
• Features: Cost-effective and rugged; handles heavy/abrasive contents; no special filling equipment needed; washable and recloseable by unsewing if needed.
• Uses: Grains, feed, seed, fertilizer, sand, and coarse powders – any bulk good where a manual sew-shut is acceptable and airtight seal is not critical.

Pasted Valve Multiwall Paper Bags

Pasted valve bags are a special type of multiwall bag designed for fully automated, high-speed filling of powders and granules. Unlike open-mouth bags, a pasted valve bag has a built-in filling spout (valve) on one side of the bag. During manufacture, one corner of the bag body is formed into a small tube or pocket and glued at the base. This “valve” is pre-pasted shut. To fill the bag, machines inject material through this valve spout. When the bag is released, the product pressure forces the valve opening to close automatically, often aided by gravity or a clamp.

Because the filling is done through the valve, the top of the bag is otherwise fully glued or sealed at manufacture (no large open mouth remains). A pasted valve bag typically has a 100% pasted bottom (like a BBOM) and an additional valve tube. After filling, sometimes the valve itself is tucked in or stitched closed. The design allows extremely fast filling (thousands of bags per hour) since the machine does not have to stop for a sealer – the bag seals itself as it comes off the line.

• Structure: Corner valve pocket (pre-glued) on one side; fully pasted bottom.
• Closure: Valve seals by pressure of contents; sometimes auxiliary clamping or stitching of the valve tip.
• Features: Superb dust control; very high throughput; consistent volume fill; minimal operator handling.
• Uses: Cement, chemicals, minerals, dry food ingredients, and any fine powder where ultimate filling speed and dust containment are needed.

Compared to PBOM bags, valve bags can fill even faster because they avoid any post-fill sealing step. However, they lack the large printable front panel of an open-mouth bag, and require specialized filling spout attachments. In practice, valve bags shine in continuous automated plant lines (cement plants, fertilizer mills), whereas open-mouth (PBOM/SOM) bags are preferred in batch or mid-speed operations.

Satchel Bottom Open Mouth (Webb Pinch) Multiwall Paper Bags

Satchel bottom open mouth bags, sometimes called Webb pinch bags, combine the square base of a block-bottom bag with the heat-sealed top closure of a PBOM bag. In a Webb pinch bag, the bottom is formed like a satchel or square pouch (all layers glued flat), creating a rigid cube. The top is open until filled, but then closed by the same pinch-heat seal technique used in PBOM designs.

This hybrid style yields the best of both worlds: a full block bottom ensures maximum volume and pallet stability, while the pinch-fold top ensures an airtight, dust-proof seal. Satchel-PBOM bags maintain the same footprint as a PBOM bag but have completely vertical sides, meaning slightly more capacity inside. Because the bottom corners are not pinched, they do not pinch inward during filling, giving a boxier filled shape.

• Structure: Pre-pasted square “satchel” bottom; open top with pre-applied heat-seal adhesive.
• Closure: Pinch heat-sealer on top flaps after filling (same as PBOM).
• Features: Even better stacking and cube utilization than PBOM; fully sift-proof closure; sturdy for heavy loads.
• Uses: High-end packaging for chemicals, food, and pet products where maximum product protection and pallet efficiency are required.

Satchel-bottom pinch bags are less common than regular PBOM or BBOM, but they are chosen when both ease of palletizing and top-seal integrity are critical – for instance, export-grade flour or premium pet food. These bags palletize more cleanly than standard PBOMs because their tops end flat, and nothing is perched above the pallet’s top layer.

Comparison of Multiwall Bag Styles

Each multiwall style has unique strengths. PBOM and Satchel-PBOM bags excel in sealing and speed; BBOM and SOS bags excel in load stability; SOM bags excel in simplicity and cost; and PV bags excel in throughput and dust control. The table below highlights the structural differences and typical uses of each style for a quick overview.

Bag Type	Bottom Style	Top Opening/Closure	Notable Features	Ideal For
Open-Top (Flat Tube)	Pre-closed flat or pinch bottom; may include simple crease	Flush-cut open top; closed by sewing or tape after fill	Most basic format; can be flat or with gussets; economical	General bulk goods (grain, feed, sand) where closure can be manual
PBOM (Pinch-Bottom Open Mouth)	Pinch-folded bottom glued at factory (square base when filled)	Pre-applied hot-melt tape; pinch heat-sealed closed post-fill	Virtually airtight seal; high-speed filling; good stacking	Fine powders (flour, cement, chemicals, pet food) needing dust-tight seal
BBOM (Block-Bottom OM)	Fully pasted flat bottom (solid block)	Flush-cut open top; usually sewn or taped closed	Rigid, self-standing base; straight vertical sides	Heavy products (fertilizer, feed, grains) and retail-size bulky goods
SOS (Gusseted OM)	Block bottom with built-in side gussets; self-opening crease	Flush-cut open top; sewn or heat-sealed by user	Self-standing open; large volume; easy manual fill	Charcoal, flour, sugar, pet food – retail/consumer-ready bags
SOM (Sewn Open Mouth)	Block or pinch bottom	Flush-cut open top; sewn shut by stitching thread	Simple, no adhesive; cost-effective; reclosable	Coarse bulk materials (grains, feed, seed, building materials)
Pasted Valve	Fully glued bottom + gusseted side	Corner filling valve (pre-glued); seals itself when filled	Fastest fill; no external dust; fixed-volume fill	Cement, minerals, chemicals – very high-speed automated filling
Satchel Pinch-Bottom Open Mouth	Square satchel bottom (block)	Pre-applied hot-melt; pinch heat-sealed	Combination of PBOM and block; flat top and sides	Premium products needing sealed top and superior palletization

Each style above addresses different operational needs. For example, if speed is paramount, a pasted valve bag or a PBOM bag will outpace a sewn bag. If pallet stability is key, the flat sides of a block bottom or satchel bag create neat stacks. If dust control is critical, the heat-sealed closure of PBOM or valve bags keeps powder inside. In practice, packaging engineers choose the style that balances filling equipment, product sensitivity, and handling requirements.

VidePak’s Multiwall Kraft Paper Bag Expertise

VidePak is a leading supplier of multiwall kraft paper bags, and all the styles above are part of its offering. VidePak emphasizes top-quality materials and rigorous production standards in every bag. They source virgin kraft paper and other inputs from world-class suppliers: for example, Mondi (Europe) or leading mills (Asia) provide high-strength kraft papers, while chemical companies like BASF and Sinopec supply specialized adhesives, coatings, and polymer films. These brand-name raw materials ensure consistency and performance.

In-house, VidePak uses advanced European converting equipment (notably Windmöller & Hölscher bagging lines and Starlinger extrusion/loom machinery) to fabricate multiwall sacks with precision. The W&H bag machines fold and glue multi-ply tubes into the various bottom types (block, pinch, satchel), and apply hot-melt adhesive tape to PBOM tops. High-speed flexo printing presses apply crisp, multi-color graphics on the outer plies before bagging. In short, VidePak’s factory is fully equipped to make any of the above bag styles – from sewn open-mouth to PBOM to valve bags – at large scale.

To meet global quality expectations, VidePak strictly follows international standards like ASTM and ISO during production. For example, paper weights (basis grams per square meter) are controlled to tight tolerances, seams and welds are inspected, and finished bags are sampled for drop, burst, and seal tests. A full QC laboratory measures tear and tensile strength (ISO 1924/1974), permeability (Gurley and Cobb tests), and barrier performance on coated bags. The result is that every bag meets its design specs. VidePak documents each production lot with certificates and testing data, giving customers confidence in consistency.

Besides quality, VidePak boasts immense capacity. With dozens of multiwall and woven bag lines running year-round, VidePak can produce on the order of 600 million bags per year. This scale means they rarely run out of stock of standard sizes, and can quickly ramp up for large orders. The factory runs 24/7 on multiple shifts, and vertical integration (making their own films, tapes, and fabrics) cuts lead times. Even for custom or multi-color printed bags, VidePak’s modular presses and baggers allow fast changeovers. In effect, VidePak combines mass production efficiency with tight quality control, so customers get high volumes of reliably identical bags.

Aspect	VidePak Details
Raw Materials	100% virgin kraft paper (various grades, e.g. brown/white kraft) from leading mills (Mondi, etc.); high-purity polymer resins (PE, PP) from BASF, Sinopec, etc.; food-grade inks and adhesives from top chemical suppliers. These are batch-tested before use.
Production Equipment	European lines (W&H, Starlinger) for bag converting and printing; high-speed pinch-sealers and sewing stations; slitter/rewinders; extrusion coating and lamination facilities on site. Fully integrated from film to finished bag.
Standards & Testing	Bags built to ASTM/ISO specs (e.g. ASTM D642 drop test, F88 seal strength, ISO 2233 stack test); in-line inspections (laser, cameras); QC lab tests tear, tensile, porosity, barrier (ASTM/ISO methods); certified ISO 9001/22000 quality system.
Capacity & Logistics	~600 million multiwall bags/year; multiple parallel lines; 24/7 operation; large raw material and finished goods warehouse. Able to stock common SKUs; short lead times on standard orders.
Quality Assurance	Every batch undergoes drop/compression tests; seals are peel-tested; moisture barrier and migration tests on lined bags; final inspection ensures zero dust sift. Complete traceability and compliance documentation accompany shipments.

Production Standards and Finished-Product Inspection

Quality control is woven into VidePak’s production flow. Raw paper rolls are acclimated to factory humidity (around 45–55% RH) before converting, ensuring dimensional stability. During bag making, machines use digital sensors to monitor dimensions (bag width, gusset depth, tube flatness) within ±2–3 mm. Glue application is checked for coverage, and pinch seal equipment verifies adhesive film presence and activation.

Finished bags are put through automated and manual tests. Random samples from each batch are filled to rated weight and drop-tested from prescribed heights (e.g. 80 cm drops per ISO 2233). The heat-sealed closures of PBOM bags are peeled to confirm inner ply bonding (ASTM F88). For bags with polymer liners, integrity is checked via vacuum tests or WVTR/OTR measurements (ASTM methods). A simple “shake test” turns each sample bag upside-down to see if any dust escapes; properly produced PBOM and valve bags show zero sift. Print quality, color matching, and labeling accuracy are also verified. Only after passing all these inspections does VidePak approve a shipment.

This thorough QA regime ensures that when you fill a VidePak bag on your line, it behaves predictably. Bags arrive with full certificates of compliance: paper grammages, liner specs, test results and even roll numbers are documented. For users, this means fewer line stoppages (no unexpected weak seams) and fewer customer complaints (no spilled product or moisture damage). In short, VidePak’s commitment to standards – from raw material certificates to final inspection reports – translates into peace of mind.

Conclusion

Multiwall kraft paper bags are a versatile packaging solution across industries. Each style – whether it’s a simple open-top sack, a high-speed PBOM, a stable block-bottom, or a valve bag – is engineered to solve specific handling challenges. VidePak offers the full spectrum of multiwall bag designs, built with premium materials and precision equipment. By adhering to international standards (ASTM, ISO) and maintaining rigorous quality control, VidePak delivers bags that are strong, consistent, and fit for purpose. With massive annual capacity and end-to-end production capabilities, VidePak ensures large orders of multiwall bags are met on time and at competitive prices.

Key takeaways: VidePak’s multiwall bags use top-grade kraft paper and liners (from Mondi, BASF, Sinopec, etc.), and are produced on advanced W&H and Starlinger lines. Customers can choose from sewn, PBOM, valve, and other formats to match their filling equipment and product needs. All bags are factory-tested and documented to guarantee strength and integrity. In other words, choosing VidePak multiwall kraft bags means getting a proven packaging system – one that stands up on the shelf, seals out contaminants, and keeps your product safe from factory to customer.

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