On Tuesday's session, the natural rubber front-month settled at 20,440 yuan/t, down 1.64% on the day, while butadiene rubber (BR) closed at 15,990 yuan/t, a 2.68% drop that outpaced NR by roughly one percentage point. The NR/BR spread widened from 3,575 yuan last week to 4,450 yuan/t, back to the high end of its yearly range.

The driver is straightforward: BR's feedstock butadiene saw units restart and supply loosen, while NR stayed supported by monsoon-disrupted tapping across Southeast Asia. For a tire maker, every tonne of BR swapped into the recipe in place of NR saves about 4,450 yuan at the raw-material line, but BR's wear and heat-build characteristics cap the substitution ratio, typically floating between 15% and 35%.

Operationally, when the spread exceeds 4,000 yuan, passenger-car tire formulations tilt visibly toward BR; below 3,000 yuan they swing back to NR. The window now favors BR, but once butadiene enters its maintenance season the spread snaps back fast. Locking a slice of NR inventory through bonded warehouse receipts keeps the substitution decision in the buyer's hands.