The two rubber contracts rose together on 30 Sept but with very different force. BR gains 4.97% to 16,155 while NR adds only 3.28% to 19,665. The move widens the NR-over-BR gap from around 3,500 at month start to 3,510 — NR still commands a premium, but BR is closing faster.

The driver is upstream. Spot butadiene is tight after turnarounds at several steam crackers, with CFR North-East Asia offers firm and domestic BR operating rates squeezed by both thin margins and scarce feedstock. BR is a butadiene derivative, so the board prices the premium the moment feedstock tightens.

For tyre makers the read is plain: BR takes roughly 25%–35% of a tread compound, so the jump lifts mixing cost on both passenger and truck tyres. Eating more NR hedges for a while, but NR is also rising, so the offset is limited; the realistic move is to pre-fix some BR forward and average fourth-quarter buying.

SNSUC's listings carry real rubber offers, and an operator can package a "BR forward plus NR spot" structure for downstream — cost locked with room to flex. The 30 Sept jump is a reminder that synthetic rubber now trades off the cracker turnaround calendar, not just tyre demand.