Multiwall kraft sacks for dry bulk packaging separate into two primary construction categories: pitched/sewn open mouth bags and pasted valve bags. Structural geometry defines filling method, sealing labour cost, stacking stability, and bulk material compatibility. Selection depends on filling line automation level, bulk powder/granulate flow characteristics, palletisation requirements and landed supply chain cost per unit.
H2: Structural Differences Between Pitched Sewn Open Mouth Bags and Pasted Valve Bags
Pitched sewn open mouth sacks are manufactured with a folded, pitched bottom sealed by continuous sewing thread. The full top opening remains exposed for gravity or auger filling. Bag closure requires stitching, heat sealing, or tie-string operations after filling. Pasted valve bags integrate an internal paper valve sleeve at one corner, formed by adhesive pasting during conversion. Dry bulk product enters through the valve; internal pressure during filling self-seals the valve without secondary sealing steps.
| Parameter | Pitched Sewn Open Mouth Bag | Pasted Valve Bag |
|---|---|---|
| Bottom Construction | Pitched folded base, sewn closure | Flat pasted base |
| Filling Orifice | Full-width top opening | Corner paper valve sleeve |
| Post-Fill Sealing | Required (sew/tie / heat seal) | Self-sealing under internal fill pressure |
| Typical Ply Count | 2–4 ply kraft | 2–5 ply kraft |
| Common GSM Range | 70–120 gsm per ply | 80–130 gsm per ply |
| Burst Index | 3.2–3.8 kPa·m²/g | 3.4–4.0 kPa·m²/g |
| TEA (Tensile Energy Absorption) | 160–210 J/m² | 180–230 J/m² |
| Deckle Width Range | 380–950 mm | 350–850 mm |
For detailed construction and material options for valve sacks, review Insert Link: multiwall kraft paper valve bags.
H2: Filling Line Throughput & Labour Cost Comparison
Open mouth sacks suit semi-automatic filling lines. Operators must present the open mouth to the fill spout, then move filled sacks to a separate sealing station. Labour input is tied directly to bag handling and sealing. Pasted valve bags pair with automatic spout fillers. Operators slide the valve sleeve onto the fill nozzle; pressurised filling closes the valve upon nozzle retraction. No dedicated sealing station is needed.
| Metric | Pitched Sewn Open Mouth Bag | Pasted Valve Bag |
|---|---|---|
| Typical Line Throughput | 600–1,100 bags/hour | 1,200–2,400 bags/hour |
| Post-Fill Labour | 1 dedicated operator for sealing | Zero sealing labour |
| Filling Pressure Tolerance | Low; excess pressure causes top burst | Medium-high; designed for pressurised spout filling |
| Changeover Time | 12–20 min for size swap | 8–15 min for size swap |
H2: Material Compatibility by Dry Bulk Product Type
Flow behaviour, particle size, and abrasion determine sack construction. Free-flowing fine powders perform better in valve sacks. Flaky, low-flow or large granular materials are commonly packed in open mouth sacks.
| Bulk Material | Recommended Sack Type | Engineering Rationale |
|---|---|---|
| Cement | Pasted Valve Bag | High flow powder, pallet stacking stability; standard cement sack format, see Insert Link: valve cement bag |
| Titanium Dioxide | Pasted Valve Bag | Fine dust, minimised leakage, consistent pallet profile |
| Animal Feed Pellets | Pitched Sewn Open Mouth | Large granular feed; low pressure gravity filling |
| Agricultural Seeds | Pitched Sewn Open Mouth | Gentle gravity fill; reduced seed breakage, see Insert Link: open cement bag |
| Fine Agricultural Chemical Powder | Pasted Valve Bag | Low dust emission, controlled fill volume |
H2: Cost Efficiency Matrix & Minimum Order Quantities
Unit sack cost and total operational cost are separate metrics. Valve bags carry a higher ex-factory unit cost due to additional converting steps for valve pasting. Open mouth sacks reduce blank paper and conversion cost but add ongoing sealing labour expense.
| Commercial Metric | Pitched Sewn Open Mouth Bag | Pasted Valve Bag |
|---|---|---|
| Ex-Factory Unit Cost Baseline | Lower | Higher |
| MOQ Standard | 50,000 sacks | 100,000 sacks |
| 40HQ FCL Approx. Load | 420,000–520,000 units (depends on dimensions) | 380,000–480,000 units (depends on dimensions) |
| Storage Stacking Performance | Moderate, uneven filled profile | Superior, uniform cuboid stack |
| Print Flexography | Up to 4 colours | Up to 4 colours |
H2: FAQ
H3: What is the MOQ difference between open mouth and pasted valve kraft sacks?
MOQ for pitched sewn open mouth sacks starts at 50,000 units. Pasted valve sacks require 100,000 units minimum due to dedicated valve converting setup. Smaller trial runs available with plate setup fees.
H3: Can both open mouth and valve multiwall sacks be printed with flexographic graphics?
Both sack styles support up to 4-colour flexographic printing. Ink adhesion and rub resistance are tested per TAPPI T830. Plate cost applies for custom artwork on both designs.
H3: What moisture protection options are available for ocean shipment of dry bulk sacks?
PE film inner liner or moisture barrier lamination can be integrated into 2–5 ply construction. All sacks are packed on heat-shrink-wrapped pallets for container transit humidity control.