Air conditioning cools room air. A mattress product acts at or around the bed, and passive cooling fabric does not remove the room’s heat load. These are different tools.
When the room needs attention
If the bedroom stays hot before you get into bed, start with room conditions. Bedding cannot make a dangerously hot room safe. An under-cover airflow system uses room air and has room-temperature limits; it is not a substitute for refrigeration.
When the bed is the remaining problem
If the room is comfortable but a heavy duvet traps warmth, lighter covers may be enough. A water-based system can provide adjustable bed temperature but needs equipment, routing and care. A passive pad or foam topper offers neither selectable temperature nor a guaranteed overnight cooling result.
Compare the full setup
Room air conditioning needs a suitable installation and operating arrangement. Bed systems need their approved equipment space and bedding layers. Consider noise, electrical requirements and maintenance for each. No universal energy-saving claim is made here: energy use depends on the exact devices, settings, room and duration.
See the cooling mattress pad buying guide for manufacturer-linked examples and the differences between fabrics, toppers and powered systems.
See Also
If you are still weighing both sides of this matchup, keep going with Fans for a Hot Bed: Room Airflow or BedJet?, Bedside Fan Placement: Height, Clearance and Cord Checks, and Portable Dehumidifier vs Whole-Room Dehumidifier.
To widen the decision beyond this head-to-head, How to Stop a Humidifier from Over-Humidifying Your Room and Best Mattresses for Every Sleep Style provide the broader context.