A method and apparatus for the formation of double-walled containers includes two integrally connected containers extending in the same direction with an air gap between them, stretch-blow moulded as single bodies out of thermoplastic material, and suitable for mass-production. A thermoplastic tubular blank is formed and then heat-conditioned. The heat-conditioned tubular blank is then mechanically stretched longitudinally and blow-formed outwards by gas pressure to form first and second containers. A piston and mould cavity cooperate to further mould the containers such that the second smaller container side wall(s) are at least substantially not in contact with the second container shaped mould cavity set and may be inverted inside-out, while the second smaller container bottom wall at least substantially does not invert, in order for the second smaller container to become a substantially mirror-image inverted second smaller container extending in the same direction as, and interior to, the first container.