Thermal Cycler is a laboratory apparatus used for PCR. The device has a thermal block with holes where tubes with the PCR reaction mixtures are inserted. The cycler then raises and lowers the temperature of the block in discrete, pre-programmed steps. Thermal cyclers are equipped with a hot bonnet, a heated plate that presses against the lids of the reaction tubes. This prevents condensation of water from the reaction mixtures to the insides of the lids and makes it unnecessary to use PCR oil.