Natural rubber front-month closed at ¥18,800/t today, up 0.27% on the day, while butadiene rubber settled at ¥14,660/t, down 0.2%. Their spread widened from roughly ¥3,900/t last week to ¥4,140/t, back to the high range last seen in the second quarter.

The driver is on the supply side. Butadiene rubber operating rates have recovered as two 120-kt/yr plants in North China restarted after maintenance, pushing social inventories higher for three straight weeks. Natural rubber, by contrast, faces the tail of the Yunnan tapping season and a mismatch in port arrival timing, leaving deliverable warehouse receipts thin. One leg rises, the other falls, and the blend-cost balance tilts toward synthetic rubber.

For tire makers this is a hard signal to rotate recipes. Every 5-percentage-point increase in butadiene content in a full-steel tire can cut green-rubber cost by about ¥6–8 per tire; once the spread exceeds ¥4,000/t, compound engineers typically push butadiene to the contract ceiling. Passenger-car tires hold butadiene content more rigidly for performance reasons and barely react to the spread, but full-steel lines accelerate butadiene purchasing visibly.

Operationally, SNSUC's digital warehouse-receipt quotes for physical natural rubber track the front-month future, so traders can lock the spread at its high and run inter-month swaps against bonded receipts; downstream tire makers should price butadiene in tranches during the dip rather than chase it when the spread narrows. The current structure favors buyers and should hold until Southeast Asian peak-season arrivals hit in October.