Why Soda or Soft Drink bottles not filled completely?

 The soft drinks were filled in bottles made up of glass or plastic. The gas were filled in the bottles by compressing them under the room temperature but when the soft drinks were chilled at sub zero temperature the water in the bottle starts to expand which needs a gap for expanding in the bottle made up of plastic or glass. The Soda bottles have rich amount of CO2 gas which filled by compressing at warmer temperature.

                                                                 

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