Mumbai: Shares of container and packaging makers continued their winning run on Monday following the strength in speciality chemical prices including that of BOPP (Biaxially Oriented Poly Propylene) films. Shares of Cosmo Films, Jindal Poly films and Uflex surged 4-8 per cent on Monday.B&K Securities said BOPP prices in February surged 16 per cent from the previous month on account of supply constraints and an increase in raw material prices. Experts said supply shortage has led to an improvement in the spreads.On Monday, Jindal Poly Films’ shares hit a 52-week high of Rs941.25 before ending up 7.2 per cent at Rs 917.30. Cosmo Films’ shares also hit a one-year peak of Rs 697.85 before ending 4 per cent higher at Rs 681.50. Uflex ended up 5.3 per cent at Rs 438.65 after hitting a 52-week high of 446.05.The stocks have shot up in the past month, with Jindal Poly gaining 84 per cent during the period. Uflex has gained 23.4 per cent and Cosmo Films is up 33 per cent in the last one month. Jindal Poly has also surged on reports that the company is looking at selling a minority stake to raise as much as Rs 1,000 crore to Rs 1,200 crore as the BC Jindal group company looks to take advantage of frenzied investment activity in the packaging industry.However, experts believe these gains are not sustainable. “These are cyclical stocks where every two-three years the cycle turns positive. But it is not sustainable going by the history of these cycles. They cannot be valued as growth stocks,” said independent market expert Sandip Sabharwal. “People who are looking to buy them at a time when margins are the highest will tend to lose money. All of them are overvalued.”The government has also issued a draft regulation that may lead to a ban on single-use plastic for candy and ice cream sticks and film wraps around sweet boxes and cigarette packets.