Method of moulding and mould tool

A mould layer assembly for insertion into a mould tool, comprising:

• a first mould layer defining a first mould surface;
• and
• a second mould layer defining a second mould surface opposite the first to define a mould cavity;
• wherein at least the first mould layer comprises a series of fluid chambers opposite the first mould surface, which series of fluid chambers define a plurality of tessellating zones, zones;
• a pin defined on the first mould layer;
• a catch defined on the second mould layer, wherein the catch is rotatable, defines a mouth receiving the pin and has a locus moving inwardly towards its axis of rotation, the catch being resiliently biased;
• wherein as the first mould layer and the second mould layer are clamped together in a moulding operation, the catch is configured to rotate under the resilient bias to drive the mouth further over the pin and at least partially maintain an applied clamping force between the first and second mould layers.