New Delhi: The government has approved the introduction of one billion polymer banknotes of Rs 10 and Rs 20 for field trials, Parliament was informed on Tuesday. As per the RBI, these polymer banknotes are proposed to be issued along with paper substrate-based banknotes," she said. The RBI has informed that the procurement process is presently at an initial stage, she said. Therefore, she said, at this point of time, it would not be possible to practicably determine the exact timeframe for introduction of polymer banknotes or the expenditure likely to be incurred thereon. However, she said, it is still below the Reserve Bank of India's inflation target of 4 per cent.