Quick answer: Paper weight decides which bag a line can make. V-bottom lines run the lightest papers (35–80 GSM), standard square-bottom lines run 50–150 GSM, and economy square-bottom lines stretch to 160 GSM. Match the machine’s GSM window to your paper supplier’s stock before you buy the line — paper is 70–80% of your variable cost, and the mismatch is the most common first-year mistake.
Buyers spend weeks comparing machine specs and an afternoon choosing paper. That ratio is backwards: after labour, paper is the largest running cost of a bag business, and each machine line accepts only a specific GSM and roll-width window. Here is how the numbers fit together.
What GSM means for a bag maker
GSM (grams per square metre) is paper weight per area. In bag making it tracks directly with strength, stiffness and cost:
- 35–60 GSM — light, flexible sheets for bakery bags, sandwich bags and produce bags. Runs fast; tears if overloaded.
- 60–100 GSM — the workhorse range for takeaway and light retail bags; food-safe kraft is widely available here.
- 100–160 GSM — heavy carriers that hold bottles and canned goods without handles stretching or bases failing.
Machine data confirms the split. VJD V-bottom lines are specified for 35–80 GSM — they form side gussets from light paper at high speed. VFD square-bottom lines handle 50–150 GSM on the standard series and 50–160 GSM on the economy F-series, because a flat, load-bearing base needs stiffer sheet.
Roll width is the second number nobody checks
Every machine accepts a roll-width window, and your paper mill must cut to it. VFD standard models take rolls from 320 mm up to 1300 mm depending on model; VJD lines are sized to the tube width of the bags you print. A 50 mm mismatch between your paper stock and the machine window means either a re-order or a narrower bag than your customer asked for.
Two practical rules:
- Buy paper after the machine order is placed, against the machine’s stated roll-width window and core size.
- Ask your mill for tolerance in writing — width and GSM tolerance drift shows up as bag-length variation on the machine.
Food-grade is a paper choice, not a machine setting
Machines form, glue and cut; the food-safety status lives in the paper and glue. If your bags touch ready-to-eat food (bread, snacks, produce), specify food-grade kraft from the mill and a food-safe glue system when ordering the line. Fruit bag lines are a dedicated case: VFB fruit-protection models work with vented, food-safe kraft in lighter GSM ranges — the paper spec is set by the orchard’s standards, not the machine.
Reclaimed, virgin, or blended?
- Virgin kraft — highest strength per GSM; the safe pick for heavy carriers and any bag above ~120 GSM.
- Recycled kraft — lower cost and a sustainability story; strength per GSM is lower, so step up one GSM class for the same bag duty.
- Blended — the common middle ground for takeaway and grocery bags.
Whichever you choose, re-run a small test batch on the machine whenever the mill changes the furnish — recycled content shifts are the usual culprit behind sudden sheet breaks.
How paper cost drives the ROI math
Because paper is 70–80% of variable cost, your local kraft price per ton moves the break-even point more than machine speed does. A line running 30 bags/min on cheap, reliably-supplied 70 GSM stock can out-earn a faster line starved of the right paper. Work the four numbers — output, material, selling price, labour — in our paper bag ROI guide before committing to a configuration.
FAQ
What GSM do grocery carriers use?
Typically 100–160 GSM square-bottom bags with handles; lighter grocery formats run 70–90 GSM without handles.
Can a square-bottom machine run light 40 GSM paper?
Not recommended — the forming and base-folding units are set for stiffer sheet. Use a V-bottom line for that range.
Does heavier GSM slow the machine?
Within the machine’s window, no meaningful slowdown; outside it, expect feed and fold faults. That is what the GSM window exists to prevent.
What is the lead time for a paper bag line?
Lead times run 7–45 days depending on the machine, with a 2-year warranty and lifetime technical support.
Next steps
Check bag types in the paper bag machine types guide, see where each paper class is used in the production line guide, then shortlist models in the buying guide.