Are bamboo or eucalyptus sheets actually cooler than cotton?

Reviewers consistently describe both fibers as cool-to-the-touch and silky, and a Qmax measurement of around 0.4 cited in r/BedroomBuild discussion supports that. However, r/Bedding commenters repeatedly note that lyocell and viscose feel cool initially but can trap heat under heavy bedding, and that crisp cotton percale or linen may breathe better for true hot sleepers. Expect 'silky and cool to touch' more reliably than 'sweat-proof in a hot room.'