Cost

Blow Molding Cost per Bottle: Building a Defensible Quote

What actually drives cost per blow molded bottle and how to build a quote that holds up: resin, machine time, labor, scrap, and tooling amortization.

On a commodity HDPE bottle, resin is 55 to 70 percent of piece cost, so start there. Resin Cost per Bottle equals parison weight times resin price, not finished weight. At HDPE around 1.35 dollars per kg and a 36.4 g parison, gross material is 0.0491 dollars. If in-house regrind offsets 90 percent of the 4.4 g flash, you recover about 0.0053 dollars, netting near 0.0438 dollars per bottle. Quoting off the 32 g finished weight instead of the 36.4 g parison understates material by 12 percent, the single most common blow molding quoting error.

Machine time is the second lever. Convert your all-in machine rate, say 55 dollars per hour including energy and depreciation, into cost per part by dividing by effective Cavitation Output. At 883 bottles per hour, machine cost is 55 / 883 = 0.0623 dollars each. Note that this uses effective, not nameplate, output: quoting on a theoretical 960 per hour instead of the real 883 undercuts you by 8 percent on the largest non-material cost. A one second cycle improvement here, 15 to 14 seconds, lifts output to 946 and drops machine cost to 0.0581, a 6.7 percent gain.

Labor rarely tracks one operator to one machine. If one operator tends 4 machines at 24 dollars per hour fully burdened, labor per machine-hour is 6 dollars, or 6 / 883 = 0.0068 dollars per bottle. Add QC and packing labor separately. The estimating mistake is assigning a full operator to each press: that would quadruple labor to 0.0272 dollars per bottle and price you out of the bid. Confirm actual machines-per-operator on the floor before you cost labor, because staffing ratios move this line by 300 percent.

Scrap is a multiplier on everything before it, not a line item you add once. If Flash Scrap Rate reflects reused regrind it barely touches cost, but true rejects, short shots, leakers, contamination, do. A 3 percent reject rate means you must make 1,000 / 0.97 = 1,031 bottles to ship 1,000, so divide material plus machine plus labor by 0.97. On a 0.113 dollars subtotal that adds 0.0035 dollars per shipped bottle. Leaker rates from the Leak Test Capacity station tell you the real number; a 5 percent leak rate is quietly a 5.3 percent cost surcharge.

Tooling amortization decides whether a small run is profitable. A 4-cavity EBM mold at 45,000 dollars amortized over a 2 million bottle program adds 0.0225 dollars per bottle; over 500,000 bottles it adds 0.09 dollars, quadrupling the tooling line. Always state the volume your quote assumes. Buyers who negotiate price down while cutting volume in half without re-amortizing tooling erase your margin. Quote tooling as either a separate one-time charge or an amortized adder tied explicitly to a minimum annual volume, never buried silently in piece price.

Overhead and yield loss round out the build. Layer plant overhead as a percentage of the direct subtotal, commonly 12 to 20 percent, then add margin on top of that. A worked stack: resin 0.0438, machine 0.0623, labor 0.0068, scrap adder 0.0035, tooling 0.0225 gives 0.1389 dollars direct. Add 15 percent overhead (0.0208) for 0.1597, then 12 percent margin for a 0.179 dollars quote. Show the buyer the stack; a transparent quote wins more than a low opaque one and protects you when resin moves.

Resin price volatility is the risk you must hedge in the quote. HDPE and PP have swung 30 to 40 percent inside a year. Since resin is 55 to 70 percent of cost, a 30 percent resin jump on a 0.179 dollars bottle adds roughly 0.013 dollars, a 7 percent price hit. Build a resin escalator clause tied to a public index and reprice above a 5 percent move. Estimators who lock a 12 month fixed price with no escalator on a resin-heavy part are betting the whole margin on the polymer market.

Validate the quote against a simple sanity ratio before sending. For commodity HDPE bottles, material should land near 55 to 70 percent of factory cost, machine plus labor near 25 to 35 percent, and tooling plus overhead the remainder. If your material fraction comes out at 40 percent, you either understated parison weight or overstated machine rate. Cross-check parison mass with the Parison Weight calculator and output with Cavitation Output, then confirm Resin Cost per Bottle independently. A quote that fails the ratio check almost always has a hidden input error.

Published 2026-07-01.