Wax is the oldest thermoplastic material known to man and originally beeswax was used, but today the name ‘wax’ applies to any substance having wax-like properties.

Modern blends of investment casting wax are complex compounds containing numerous components :

• hydrocarbon wax
• natural ester wax
• synthetic wax
• natural resins
• synthetic resins
• organic filler materials
• water
  

Hydrocarbon wax, natural ester wax, many types of synthetic wax, and some of the resins used are compounds of straight chained carbon atoms (aliphatic compounds).
Additionally some of the other resins and filler materials used are compounds of ring structured carbon atoms (aromatic compounds).

Fundamentally the length and the complexity of the carbon chains of the various components influences the properties of the final wax. Accordingly many variations are formulated to suit differing foundry requirements and key properties such as melting point, hardness, viscosity, expansion and contraction, setting rate, etc are all influenced by the structure and composition of the wax compound.

The complex composition of modern wax products manifests itself in a physical behaviour different to that of other substances. Unlike other homogeneous chemical compounds, wax does not melt immediately on heating but passes through several intermediate states :

Similarly the structure and components used in an investment casting wax will influence the expansion and contraction characteristics:

• Like other materials wax expands on heating and contracts on cooling
• In comparison with a metal the expansion is relatively high
• Wax expansion and contraction rates are not uniform but vary with phase and structure changes during heating/cooling