Polyethylene Flat Bag Buying Guide
What Are Polyethylene Flat Bags?
Polyethylene flat bags (also called poly flat bags or lay-flat poly bags) are the most common type of plastic packaging bags. Unlike gusseted bags with expandable sides, flat bags have two layers of polyethylene film heat-sealed on three sides with one open end. They're ideal when you need simple, cost-effective protection for products that don't require expansion room.
LDPE vs LLDPE: Which Type Do You Need?
Low Density Polyethylene (LDPE) bags offer excellent clarity, flexibility, and tear resistance. They're softer to the touch and work well for retail packaging, food service, and applications where you need to see the contents clearly.
Linear Low Density Polyethylene (LLDPE) bags - like our TUF-R® line - provide superior puncture resistance and tensile strength at the same thickness. Choose LLDPE when packaging sharp-edged items, heavy products, or when you need maximum durability at a lower gauge (which saves material costs).
Understanding Mil Thickness
| Thickness |
Best Uses |
Example Products |
| 0.9-1 mil |
Lightweight protection |
Baked goods, apparel, documents, small parts |
| 1.25-1.5 mil |
Standard duty |
Food products, hardware, retail merchandise |
| 1.8-2 mil |
Heavy duty |
Industrial parts, bulk items, frozen foods |
| 2.75-4 mil |
Extra heavy duty |
Sharp objects, heavy hardware, construction materials |
| 6 mil |
Maximum protection |
Metal parts, machinery components, long-term storage |
Polyethylene Flat Bags: Frequently Asked Questions
What is a polyethylene flat bag?A polyethylene flat bag is a two-panel plastic bag heat-sealed on three sides with one open end and no gusset or expandable side panels. Prism Pak stocks flat poly bags in low density (LDPE) and linear low density (LLDPE) film from 0.9 mil to 6 mil, in hundreds of sizes from small 2x3" bags up to large industrial dimensions. Are polyethylene flat bags food safe?Yes. Our polyethylene flat bags from LK Packaging are manufactured from virgin polyethylene resins that meet FDA requirements for direct food contact, which makes them suitable for bakery items, candy, nuts, coffee, frozen foods, and other food packaging applications. What is the difference between LDPE and LLDPE flat bags?LDPE flat bags offer better clarity and a softer, more flexible feel, while linear low density (LLDPE) bags such as the TUF-R® line deliver higher puncture resistance and tensile strength at the same thickness. Choose LLDPE for sharp-edged or heavy items, since it often lets you drop to a lower gauge and save on material cost. What mil thickness do I need for a poly flat bag?Use 0.9-1 mil for lightweight items like baked goods, apparel and documents; 1.25-1.5 mil for food products, hardware and retail merchandise; 1.8-2 mil for industrial parts, bulk items and frozen foods; 2.75-4 mil for sharp objects and heavy hardware; and 6 mil for metal parts, machinery components and long-term storage. Can you heat seal polyethylene flat bags?Yes. Polyethylene flat bags seal easily with impulse sealers, hot bar sealers, or heat tunnels, typically at a sealing temperature of 275-350°F depending on the film thickness. What is the difference between a flat poly bag and a gusseted poly bag?A flat bag has only two dimensions, width and length, with no expandable sides, while a gusseted poly bag has folded side panels that open out to hold bulkier products. Flat bags cost less per bag and are the better choice for thin or flat items. What size poly bag should I order?Measure your product's width and length, then add 1-2 inches to each dimension so the bag loads and seals easily - an 8x10" item fits best in a 10x12" bag. If you also need help picking a gauge, see our guide to choosing the right bag thickness. Who uses polyethylene flat bags?Bakeries, food service operations and food processors use them for baked goods, candy, nuts and frozen product; retailers and e-commerce sellers use them for apparel and merchandise; and manufacturers, distributors and repair shops use the heavier 2-6 mil gauges for hardware, industrial parts and long-term storage. Do you offer custom printed polyethylene bags?Yes. We print logos, product information and branding on polyethylene bags in quantities as low as 10,000 pieces. See Prism Pak custom bags or contact us for a custom printing quote. Alternative Bag Options
Not sure flat bags are right for your application? Consider these alternatives:
Free Shipping on Orders Over $250
Get free ground shipping on all wholesale polyethylene bag orders over $250 to the continental US. Most orders ship same-day from our Pennsylvania distribution center.
Questions? We're Here to Help
Not sure which polyethylene flat bag is right for your application? Our packaging experts can recommend the ideal thickness, size, and material for your needs. Call 1-800-976-BAGS (2247) or contact us online.
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