Media Type
XAVC S 4K (100 Mbps): SDHC Memory Card (4 GB or over, UHS-I U3 or Higher)/SDXC Memory Card (UHS-I U3 or Higher), XAVC S 4K (60 Mbps): SDHC Memory Card (4 GB or over, Class 10 or Higher)/SDXC Memory Card (Class 10 or Higher), XAVC S HD: SDHC Memory Card (4 GB or over, Class 10 or Higher)/SDXC Memory Card (Class 10 or Higher), AVCHD, Still: Memory Stick PRO Duo™ (Mark 2), Memory Stick PRO-HG Duo™, Memory Stick XC-HG Duo™, SD/SDHC/SDXC Memory Card (Class 4 or Higher)
Needs to be that type in order to support highest quality 4k. Sandisk is pretty much defacto brand to go with but never had a problem with Samsung, Sony, Kingston, PNY...etc. Make sure you get it from a reputable seller cause there are known counterfeits out there.