Base elements → Materials → Organic materials

CORK

Table of main properties of cork

 

Property Typical Value Remarks
Density ~0.12–0.25 g/cm³ Very low
Young’s modulus (E) ~0.01–0.05 GPa Extremely low
Tensile strength ~1–5 MPa Very low
Hardness (HV) Not applicable Soft organic material
Thermal conductivity ~0.03–0.05 W/m·K Very low (excellent insulator)
Electrical conductivity Very low Insulating material
Thermal expansion Very low Good dimensional stability
Melting point Not applicable Decomposes when heated
Magnetism No Non-magnetic
Corrosion resistance Excellent Resistant to moisture and chemicals
Machinability Easy Cutting, shaping, compressible

Cork is a natural material derived from the bark of the cork oak (Quercus suber), characterized by a closed-cell structure that is lightweight and compressible. In watchmaking, its use is now very limited, but it was historically used for specific applications, particularly in sealing systems.

Its compressibility, elasticity, and relative impermeability made it a valuable material at a time when modern solutions (polymers, elastomers) were not yet available.

Main Properties

Cork exhibits the following characteristics:

  • Very low density (~0.1–0.3 g/cmÂł)
  • High compressibility and elasticity
  • Good damping capacity
  • Low thermal conductivity
  • Relative impermeability to liquids
  • Non-magnetic material
  • Good resistance to natural aging (under certain conditions)

These properties explain its historical use in sealing functions.

Cork is composed of:

  • Gas-filled cells
  • Cell walls rich in suberin (a hydrophobic substance)

This structure gives it:

  • High compressibility
  • Partial elastic recovery
  • Good resistance to moisture

However, it remains:

  • Sensitive to mechanical wear
  • Less stable than modern materials

1. Seals (Historical Use)

Cork was used in early waterproof watches for:

Function:

  • Providing sealing through compression
  • Compensating for surface irregularities

👉 These uses are now obsolete, replaced by:

  • Rubber
  • Synthetic elastomers
  • Technical polymers

2. Straps (Anecdotal Use)

More recently, cork has been used marginally for:

Characteristics:

  • Lightweight
  • Flexible
  • Natural appearance

👉 Very limited use in watchmaking.

Advantages

  • Very lightweight
  • Compressible
  • Good damping capacity
  • Natural material
  • Non-magnetic
  • Relative impermeability

Limitations

  • Low mechanical strength
  • Rapid wear
  • Aging (drying, cracking)
  • Limited sealing performance
  • Replaced by modern materials
  • Very marginal use today