Do you put underlay under Karndean?

Do you put underlay under Karndean? Depends on Karndean type, with Karndean Korlok rigid click LVT having built-in acoustic backing so no additional underlay needed, while Karndean glue-down Knight Tile and Van Gogh require no underlay as glued directly to subfloor, with Karndean official guidelines saying no underlay for glue-down as it would prevent adhesion, though for click Korlok you can use thin underlay if recommended but built-in pad usually sufficient. Karndean glue-down LVT like Van Gogh, Knight Tile, Opus, and Da Vinci are glued directly to prepared subfloor with Karndean approved adhesive, no underlay under as underlay would prevent bonding and cause failure, with subfloor needing to be flat and dry. Karndean Korlok is rigid core click LVT with integrated acoustic foam backing that provides cushioning and sound insulation, so no separate underlay needed, though some installers use thin 1mm underlay for extra soundproofing if subfloor is concrete, but Karndean says not necessary and may void warranty if thick underlay used. So do you put underlay under Karndean? No underlay for glue-down Karndean, and no extra underlay needed for Korlok as it has built-in underlay, with Karndean advising against additional underlay for glue-down and saying Korlok has integral backing, making underlay not required for Karndean flooring, with subfloor prep being flatness more important than underlay.