Here are the top recommended (fastest) SD memory cards for Sony a9 mirrorless camera.
The Sony a9 mirrorless camera comes with 24.2MP Full-Frame Sensor, 693-Point AF System & 20 fps Shooting, Internal UHD 4K Video Recording and Dual SD Slots: the card slot 1 is compatible with ultra-fast UHS-II SD memory cards while the Card Slot 2 is compatible with UHS-I memory cards. If you want to shoot 4K video with the Sony a9, a fast UHS-II SD memory card is a must. But NOT all UHS-II cards have excellent performance: the Write Speed matters, the Write Speed is the key: Fast write speed provides fast buffer clearing time between burst shots optimizing your shooting experience. Fast read speed can let large files such as 4K video or a bunch of high-resolution images by continuous shooting transfer to PC in seconds.
And, if you plan to shoot videos, stick to 64GB or 128GB (or larger) SDXC cards for the best video codex.
Below are the top recommended memory cards for Sony a9, just choose the one you need!