The two rubber lines diverged tonight. Butadiene rubber at ¥15,635/t, down 2.31%, left natural rubber at ¥19,760/t (down 0.48%) behind. The NR-BR gap widened from 3,855 in the morning to 4,125 — a ¥270 expansion in a single session.

The steep butadiene drop traces to weaker butadiene monomer and tire-makers' compound substitution. In passenger-car tires BR and NR are interchangeable at adjustable fill ratios; once the gap opens, compounders cut BR toward its floor and load more NR. That shift is already underway — NR's resilience is not its own strength but demand pulled in by the compound math.

For NR traders the widening gap cuts both ways: physical moves well, but the pricing exposure grows. We lock stock on bonded warehouse receipts — 50,000 tonnes of NR is about ¥988m of value, and with receipt pledging compressed from T+3 to T+0 the encumbrance releases on the trade day, lifting turnover from 9x to over 10x. Lock the stock without locking the position; that is the point.

The downstream signal is clear: do not chase BR shorts, the gap has already priced the bearish leg in; on the NR side watch the restocking rhythm, because substitution demand can lift the near-month basis. Reconcile the receipt book and the physical book tonight — they should match.