The rubber complex firmed across the board on 31 August: natural rubber at RMB 18,905/t (+0.51%) and butadiene rubber at RMB 14,435/t (+0.31%), holding the natural-to-synthetic spread at RMB 4,470/t. On supply, Thailand and Indonesia have entered peak tapping season and theoretical output is rising, but intermittent rainfall has made cup-lump arrivals uneven and kept latex prices firm, underpinning the market. On demand, tyre OEM orders and replacement-market offtake are restocking together, easing finished-goods inventory pressure and shifting buyers from wait-and-see to dip-buying, which nudged spot transaction levels higher. Synthetic rubber was flat at RMB 13,613/t and an alternative natural-rubber quotation was also unchanged at RMB 16,968/t, showing persistent structural gaps between delivery standards and regional benchmarks. SNSUC Research Institute notes that natural and butadiene rubber both sit within the platform's 13 core commodity categories, and with the spread in the upper-middle of its historical range there is genuine economics for synthetic substitution in compounding; should natural rubber keep rallying while butadiene lags, substitution ratios could rise further. Buyers are better served by a combined strategy - locking base volumes in natural rubber while topping up flexibly with synthetics - rather than concentrating in a single grade, while watching September rainfall and shipping schedules for arrival-pace effects.