Flexible, liquid fillable bottles of polyester resin are provided which have a capacity in liters relative to the weight thereof in grams excluding the neck of from 0.15 to 0.5 and from 0.2 to 1.5 for larger capacities. The bottles are obtained by blowing parisons freely or in a rigid container, the shape of which the bottles assume, said parisons being of polyester resin with suitable rheological properties.