Quick Answer: For polyethylene pellet and agricultural bags: bags up to 5 kg need 80–100 microns; 5–15 kg need 100–120 microns with reinforced bottom seams; 15–25 kg (the standard commercial pellet bag) need 120–150 microns with gusseted side walls. Always use fully sealed film for dried products like wood pellets, and micro-perforated film for products with residual biological activity like fresh grain. Custom flexographic printing is a legal requirement in many agricultural product categories in the EU.
The packaging requirements for bulk dry products — pellets, grain, animal feed, flour, seeds, and similar agricultural goods — are fundamentally different from consumer packaging. Where consumer bags prioritise appearance and print quality, agricultural and industrial bulk bags must prioritise structural integrity, moisture resistance, and performance under the physical stresses of filling, handling, stacking, and transport.
Getting the specification wrong in this category directly causes product loss, contamination, and operational disruptions. This guide covers the key decisions you need to make when specifying packaging for pellets and agricultural produce.
Weight and Fill: Starting With What Goes Inside
The most fundamental input for bulk bag specification is the fill weight. The table below provides starting-point ranges for polyethylene bags — actual requirements depend on product density, fill method, and handling conditions.
| Fill Weight | Min. Film Thickness | Seam Specification | Wall Construction | Typical Products |
| Up to 5 kg | 80–100 microns | Standard weld seams | Flat or simple gusset | Home pellet packs, flour, seeds |
| 5–15 kg | 100–120 microns | Reinforced bottom seam | Flat or gusseted | Animal feed, grain, fertiliser |
| 15–25 kg | 120–150 microns | Reinforced all seams | Gusseted side walls | Commercial pellets, potatoes, onions |
| 25 kg+ | Woven / laminated | Heat-sealed or sewn | Heavy-duty construction | Bulk grain, industrial materials |
Table 6: Polyethylene bulk bag specification by fill weight. Source: RB Plast production guidelines, Kocherinovo facility.
These are starting-point ranges, not precise specifications — actual requirements depend on product density, fill method, and handling conditions. RB Plast’s team in Kocherinovo can recommend the right specification based on your specific product and operation.
Moisture Resistance and Ventilation: Competing Requirements
Most bulk dry products need protection from moisture ingress — pointing toward a fully sealed bag with no perforations. However, some products — particularly fresh grain, certain seeds, and some types of animal feed — can generate moisture from biological activity within the bag after sealing, which can lead to mould and product spoilage if the bag has no ventilation.
For fully dried, stable products like wood pellets, a sealed polyethylene bag with no perforations is appropriate. For products with residual biological activity, micro-perforated film allows moisture vapour to escape without admitting liquid water or contamination. The perforation density must be calibrated to the product — too many perforations reduce moisture protection, too few are insufficient for ventilation.
Filling and Sealing Method: Matching the Bag to Your Production Line
Agricultural and pellet bags can be filled and sealed in several ways, and the bag specification must match your filling and sealing equipment. The most common configurations are: open-mouth bags filled by gravity or auger and sealed by heat sealing after filling; valve bags, where product is injected through a self-sealing valve; and pre-formed bags with zip or fold-over closures for products opened and resealed by end users.
Open-mouth bags with heat sealing are the most common format for polyethylene pellet bags in Bulgaria and the wider regional market. They are simple to fill, seal reliably with standard heat-sealing equipment, and can be printed before or after filling. Bag width, gusset dimensions, and opening configuration must all match your filling equipment precisely.
Printing on Bulk Bags: Practical Considerations
Printed bulk bags — showing product name, brand, weight, usage instructions, safety warnings, EU regulatory compliance marks, and contact information — are a legal requirement in many product categories under EU packaging regulations, and a strong commercial advantage in all of them.
Flexographic printing on polyethylene bulk bags allows up to several colours and can include both regulatory text and brand graphics. For bags exposed to outdoor conditions — such as pellet bags on outdoor displays at garden centres or agricultural merchants — UV-stable inks should be specified to prevent fading. Print registration precision is critical for bags filled on automated lines, where regulatory text and weight declarations must appear in the correct position on the finished, filled bag.
Storage, Stacking, and Logistics Performance
A bag that performs well when individual and empty may behave very differently when stacked six pallets high in a warehouse for four weeks. Key factors affecting stacking performance: film thickness and strength, gusset design (distributes load and prevents inward collapse under compression), seam strength and consistency, and the slip properties of the exterior film surface — too much slip creates unstable stacks; too little causes handling issues on automated lines.
If your product will be palletised and stretch-wrapped for distribution, bags must also be dimensionally consistent — irregular bags create unstable pallets that shift in transit, causing product damage and delivery complaints.
Frequently Asked Questions
Q: What thickness do I need for a 15–25 kg pellet bag?
A: For 15–25 kg polyethylene pellet bags — the standard commercial distribution format in Bulgaria — specify 120–150 microns with reinforced weld seams and gusseted side walls. The exact specification depends on product density and how the bags will be handled. RB Plast’s technical team can confirm the right spec for your product.
Q: Should I use perforated or sealed bags for grain and agricultural products?
A: Dried, stable products like wood pellets should use fully sealed bags with no perforations. Fresh grain, some seeds, and certain animal feeds that continue to respire after packaging require micro-perforated film to allow moisture vapour to escape and prevent mould. Consult your packaging manufacturer if you are unsure which applies to your product.
Q: Is printed packaging a legal requirement for agricultural products in Bulgaria?
A: Yes, for most agricultural and food products sold in Bulgaria and the EU, labelling requirements apply — including product name, net weight, producer details, and relevant safety information. These must appear on or with the packaging. Custom-printed bags produced by RB Plast can incorporate all required regulatory text alongside brand graphics.
Q: Does RB Plast produce pellet bags and agricultural sacks?
A: Yes. RB Plast manufactures polyethylene bags for pellets, grain, vegetables, and other bulk dry products at its production facility in Kocherinovo, Bulgaria. The company produces bags to custom dimensions, specifications, and print designs. Contact sales@rbplast.bg to discuss your requirements.
Contact RB Plast at sales@rbplast.bg or +359 887 648 950 for pellet bag and agricultural packaging specifications and pricing.
