Why are cores of inductors and transformers sometimes constructed of thin layers?

In transformers and inductors that use solid metal cores, changing magnetic fields naturally induce circulating electrical currents within the core material itself. These circulating currents are known as eddy currents. Because the metal core has electrical resistance, these eddy currents generate heat. This results in wasted energy (power loss) and can raise temperatures to damaging levels. To prevent this, cores are often constructed of thin layers, or laminations, separated by thin insulating coatings. The insulation between the thin layers acts as a roadblock, disrupting the path of the eddy currents and keeping them very small. This significantly reduces power loss while still allowing the bulk of the core to efficiently conduct magnetic flux.