Polybutylene terephthalate (PBT) pricing is frequently compared across kilograms and pounds. The specific comparison—PBT Price per KG vs per LB: Units, Basis and Why the Spread Is Not Arbitrage—requires separating deterministic mass conversion from commercial price basis. The conversion factor is fixed: 1 kg equals 2.20462 lb, and 1 lb equals 0.453592 kg. A per-pound quote is arithmetically equivalent to a per-kilogram quote only when the same resin grade, delivery term, packaging, payment condition, and testing basis are referenced. The recurring observation that a per-kilogram converted price does not reconcile with a per-pound publication is therefore not evidence of a transferable arbitrage. It is a basis mismatch between two different commercial objects.

Commercial PBT specifications are controlled by melt volumetric flow rate, intrinsic viscosity, density, moisture content, and mechanical test values. Typical unfilled injection-molding grades exhibit density near 1.31 g/cm³ when tested to ISO 1183-1:2019, melt volumetric flow rate between 10 g/10 min and 40 g/10 min at 250°C under 2.16 kg load to ISO 1133-1:2022, and intrinsic viscosity from 0.7 dL/g to 1.0 dL/g to ISO 1628-1. A per-pound price for 30 wt% glass-fiber-reinforced, flame-retardant PBT cannot be converted to a per-kilogram unfilled benchmark by mass factor alone, because the compound has different density, melt rheology, tensile strength, flexural modulus, and notched impact performance measured under ISO 527-2, ISO 178, and ISO 180/A. Those specification deltas alter legitimately priced value independent of unit arithmetic.

What Exactly Does a Per-Kilogram Versus Per-Pound PBT Quote Represent?

A per-kilogram quote from a producer or trade publication is not a simple scalar. The denominator is metric mass, but the commercial quantity may be a full truckload, container load, or break-bulk shipment. Contract prices may be listed per metric tonne, where 1 metric tonne equals 1,000 kg or 2,204.62 lb. North American distribution may use cents per pound, and the conversion from cents per pound to dollars per kilogram is (cents per pound × 0.01) × 2.20462. A short ton of 2,000 lb equals 907.18 kg, not 1,000 kg. A long ton of 2,240 lb equals 1,016.05 kg. The spread increases when a buyer incorrectly applies a short-ton denominator to a metric-tonne price.

The basis also includes Incoterms 2020. An FOB Busan quote per kilogram includes loading the resin onto the vessel at the named port. A CIF Rotterdam quote adds marine freight and insurance to the named destination. A DDP Chicago quote per pound includes import duty, customs clearance, inland freight, and often warehousing. The correct reconciliation requires subtracting those non-resin services from the delivered quote before applying mass conversion. If freight, insurance, duty, and terminal handling are not itemized, the perceived per-unit spread is not arbitrage; it is an allocation mismatch.

A compounder purchasing PBT for glass-fiber reinforced polyester production on a co-rotating twin-screw extruder with a 40:1 L/D ratio, atmospheric and vacuum venting, and a downstream side feeder cannot substitute a high-flow unfilled PBT for a high-viscosity extrusion grade solely because the converted price is lower. Screw design, residence-time distribution, and melt-temperature exposure differ by grade. The lower melt viscosity of a high-flow grade may reduce fiber breakage but also changes heat generation in the mixing zone. The compound price per kilogram and per pound is therefore coupled to processing behavior, not only to polymer mass.

Regional feedstock and duty structures further separate price bases. PBT manufacturing consumes dimethyl terephthalate or purified terephthalic acid and 1,4-butanediol. Spot fluctuations in those intermediates flow into different regional contracts at different lags depending on monthly, quarterly, or formula-linked price mechanisms. A Korean FOB per-kilogram contract may reflect one feedstock settlement period, while a US per-pound distributor list reflects a previous inventory purchase. In the absence of identical settlement timing, the unit spread cannot be arbitraged without storing resin and assuming subsequent price risk.

When Korean and Japanese Producers Quote Basis FOB Busan or FOB Kobe

When Korean or Japanese producers quote basis FOB Busan or FOB Kobe in dollars per kilogram, the quote is typically for export-grade unfilled PBT with a minimum lot of 10 t to 20 t, specified melt volume-flow rate, moisture content below 0.05 wt% at packaging, and certificates of analysis referencing ISO 1133-1:2022 and ISO 1183-1:2019. The equivalent per-pound FOB price is obtained by multiplying by 0.453592. A North American distributor quote per pound includes domestic truck or rail freight from a warehouse to the processor, inventory carrying cost, repacking from bulk into 25-kg bags or octabins, and local credit exposure. Those services are not present in the FOB numerator. When ocean freight rates and customs clearance charges move, the spread widens or narrows without changing the underlying polymer production cost. The movement is a logistics and working-capital effect, not a transferable arbitrage.

Currency adjustment is also not arithmetic. A Korean won, Chinese yuan, or Japanese yen price converted to USD may include a bank spread and forward hedging. If the per-kilogram quote is based on a monthly fixed exchange rate and the per-pound quote is spot, the apparent price gap changes with foreign-exchange volatility. That is a financial basis mismatch, not an exploitable polymer price differential. Even a correct mass conversion cannot remove it.

Why a Unit-Converted Spread Fails the Arbitrage Test

A conventional arbitrage requires purchasing one contract and selling an identical instrument or physically identical product simultaneously, with known transaction costs, and delivering against both legs. PBT per-kilogram and per-pound quotes fail this test because the material behind each quote is rarely identical. A per-kilogram export quote may describe unfilled natural PBT with a melt volume-flow rate of 20 g/10 min at 250°C and 2.16 kg, while a per-pound domestic quote may describe 20 wt% glass-fiber-reinforced PBT with an UL 94 V-0 flame-retardant classification at 0.8 mm thickness. The physical goods are not interchangeable, and blending them would change density, mechanical properties, and mold shrinkage.

Even when both quotes reference unfilled PBT, quality documentation may differ. One supplier may certify melt viscosity under ISO 1133-1:2022; another may use ASTM D1238. The two test methods use similar extrusion plastometers but differ in heat-up procedure, moisture correction, and reporting convention. A price gap attributed to units may be a test-method basis difference. The same applies to moisture specification. PBT is moisture-sensitive and will hydrolyze during melt processing. Resin guaranteed below 0.02 wt% moisture in a sealed 25-kg aluminum-lined bag after 4 h at 120°C desiccant drying has a different technical value than bulk resin with a looser moisture specification. That value difference is a processing-risk premium, not an arbitrage.

Glass-fiber reinforced PBT compounds are typically produced on twin-screw extruders with controlled side-feeding of chopped glass. Shear-induced fiber-length reduction is influenced by screw configuration, feed location, and melt temperature. A 30 wt% glass-filled PBT compound can show tensile strength above 120 MPa under ISO 527-2 and flexural modulus above 8,000 MPa under ISO 178, although published data for each commercial grade vary with fiber sizing and base resin viscosity. Because a per-pound glass-filled PBT quote includes compounding, glass fiber, and quality-control costs, it does not map onto a neat PBT per-kilogram polymer price by simple mass conversion. The spread is partly a value-added processing margin.

A delivered truckload of PBT from a US warehouse can be unloaded directly into a desiccant dryer hopper. An import container from Asia may require port drayage, de-vanning, floor-loaded bag handling, and palletization before the resin reaches the molding machine. These steps add cost per kilogram or per pound. The per-pound import price converted to per-kilogram may appear lower than the domestic quote, but after 4 h of drying at 120°C and quality preparation, the effective installed cost can invert. The spread may not even be a procurement signal until total landed cost is calculated.

On an injection-molding floor, PBT processing is bounded by a melt-temperature window of approximately 240°C to 270°C, with mold temperature typically between 20°C and 80°C. Residence time above 280°C should be minimized because the ester backbone degrades and releases tetrahydrofuran, producing black specks, reduced elongation at break under ISO 527-2, and mold deposits. A buyer who selects a per-pound lot solely because the converted per-kilogram price is lower may receive resin with broader molecular-weight distribution or insufficient drying specifications, then lose the apparent saving through purge events, rejected parts, or equipment downtime. The per-kilogram/per-pound spread is a commercial signal only after the full basis—grade, delivery term, packaging, test method, currency, and processing window—has been normalized.