Bare cast iron vs enamelled cast iron

Which one heats faster?

Neither spreads heat faster. Bare cast iron and the iron body of enamelled cast iron both conduct at about 52 W/m-K, so the difference between them lies elsewhere. Conductivity is how quickly heat moves through the metal, and at these figures the two spread a burner's heat in much the same way. Responsiveness to a change of heat depends more on thickness and mass, and there both rate low.

Conductivity is not the same as heat retention, and confusing the two is the most common misunderstanding about cookware. Cast iron conducts poorly at about 52 W/m-K and retains heat extremely well, because retention comes from mass and specific heat rather than from conductivity. That is precisely why iron sears well: the pan barely drops in temperature when cold food lands on it.

Which one suits which job?

Bare cast iron is best for searing, cornbread, shallow frying, anything that benefits from a pan that does not lose heat when cold food lands in it. Cast iron is not a good conductor. Its advantage is heat capacity: a thick, hot pan holds its temperature when a steak hits it, which is what actually produces a crust.

Enamelled cast iron is best for braises, stews, beans, bread baking and anything acidic that needs hours of gentle heat. Enamel chips if the pot is knocked or dropped, and a chipped interior on the cooking surface means the pot should be retired from cooking. It also dislikes thermal shock, so no cold water into a hot pot.

Practical differences that decide it

Induction: Both work on induction. Both behave the same way here, so it will not decide the question.

Acid: Bare cast iron is reactive, meaning long acidic cooking strips seasoning or discolours the surface, so tomato and wine braises belong in enamelled cast iron. Oven ceiling: 700F against 500F, remembering that the handle usually decides the real limit rather than the material.

Weight and upkeep: both are very heavy. Bare cast iron needs a maintained seasoning layer, which is oil polymerised onto the metal by heat, built up with use and stripped by detergent or a dishwasher.

The honest conclusion

Most kitchens should own both rather than choosing. They are good at different things, and neither is a substitute for the other. A mixed kitchen outperforms a matched one at every budget, which is the single most useful thing to understand about buying cookware.

If you genuinely have to pick one, pick on the job you do most often. For searing and browning, that is bare cast iron. For sauces and anything that needs quick control, the two spread heat at much the same rate, so choose on responsiveness and upkeep instead.