Process for producing multicellular articles

A process for the production of a multicellular stretched article, which comprises forming a blend of an orientable thermoplastics material and at least one additive, the additive comprising from more than 2 to about 50% by weight, calculated on the weight of the blend, forming a shaped article from the blend and stretching the article uniaxially or biaxially to produce a multicellular stretched article, wherein the additive is selected from metal resinates and modified or unmodified rosin esters which are at least partially incompatible with the thermoplastics material at least so that they form separate phases at the temperature at which the article is to be stretched, the thermoplastics material, when the additive is a metal resinate, being other than a crystalline polyolefin, the blend is formed by blending the thermoplastics material with the additive at a temperature at which both the additive and the thermoplastics material are molten or at least soft, and stretching is effected at a temperature within the normal orientation temperature range for the thermoplastics material, which temperature is below the softening point of the additive.