Hammersmith Bridge is being wrapped with special foil to help the 135-year-old structure stay open in the heatwave.
Engineers were seen covering chains with silver insulation to protect the Grade II listed structure in West London.
The chains, which are anchored to the river bed, are regulated to be kept under 13C in the summer. If any of them reach 18C, safety engineers will shut the bridge.
The crossing already has a temperature control system which will run throughout the night.
"The temperature control system allows us to track weather spikes and maintain a constant temperature," said project manager Sebastian Springer.
"As we deal with the current extreme heat, we are also coming up with innovative solutions to keep the temperature within the threshold," he added.
The Met Office has issued an Amber Alert with temperatures predicted to hit 34C in the borough next Tuesday.
Hammersmith Bridge was fully closed two years ago before the cooling system was installed when micro-fractures in its cast-iron pedestals widened during a heatwave.
Built-in 1887, it is one of the world's oldest suspension bridges which is why it is also one of Britain's most expensive to repair, according to the council.
The bridge is open to people walking and cycling and to river traffic beneath, but it is still closed to all motor traffic during an ongoing programme of repairs.
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