They both have their underlying conditions and are variable in values based on their backed up features.

Fiats can be devalued by the government overprinting in qualities while the excessive speculations may result to loose of purchasing power.
It can be as a result of political or regulatory manipulations to evaluate the economy system. So in a nature of economy like this, specific commodity costs which are key factors driving the global or local markets such as energies and other consumptions becomes high in price as a result of the fiats rate of purchasing power and then cost of materials becomes high right from factory. Then affordability becomes more challenging as demands becomes more competitive while supplies becomes limited.

Then is said to be inflation whereas, the fiats purchasing power is low.