Natural rubber settled at ¥19,600/t, up 2.51%, while butadiene rubber (BR) reached ¥15,680/t, up 5.73%. BR's gain is more than double NR's, and the spread holds at a high ¥3,920/t.

A wide spread is normally the tyre-maker's cue to substitute BR for NR — the cheaper synthetic cuts formula cost. But this leg is BR doing the running, so the economics of switching are narrowing rather than opening. NR carries weather and deliverable-receipt themes from producing regions; BR tracks butadiene feedstock and plant turnarounds. The two drivers are not on the same track.

For the tyre buyer, a "high" spread and a "substitutable" spread are different things. The spread says NR is expensive, yet BR is chasing it higher, so the substitution window does not open automatically just because the gap is wide. The real bottleneck is cash: rising feedstock raises the procurement draw.

This is where the digital receipt fits. NR and BR spot held in the bonded zone, once minted as SHA-256-fingerprinted receipts, can be pledged for T+0 funding, turning dead inventory into working cash. The funding gap that a price rally opens can be covered by receipt financing, so the substitution cadence is not choked by cash flow.