Do hybrid mattresses sleep cooler than memory foam?

Generally yes. The coil layer creates an airflow channel that pure foam beds don't have, and most hybrids in this roundup add a gel or phase-change cover on top. That said, very thick foam comfort layers can still trap heat even on a hybrid, so hot sleepers should look for shallower foam layers, latex, or explicitly cooling covers rather than just trusting the 'hybrid' label.