Specific heat capacity of any material = its thermal effusivity /(density*square root of (its thermal diffusivity)). That means specific heat capacity and density are always inversely proportional. This is why, as density increases, the specific heat capacity decreases and vice versa.
If you were to take a part made from steel and compare it to the same part made from thermoplastic, the plastic part could be more than 6 times lighter.
Take that same part, now manufactured with aluminum, and the plastic version would be approximately half the weight.
Strength-to-Weight Ratio
In the past, one of the biggest roadblocks to replacing metal parts with plastic was that plastic, while much lighter, could not compete with the strength characteristics of metal. Now, with advances in plastic composites and the addition of carbon fiber or other glass fibers to plastic material formulations, thermoplastic products can perform as well as and in some cases even outperform metal in ratios such as strength-to-weight and strength-to-stiffness.
Strength-to-Weight Ratio, also known as Specific Strength, is a material’s strength (force per unit area at failure) divided by its density.
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