An H2W file is a data file created by the H2testw and F3 programs, which are tools used to scan USB drives and SD cards to test their performance and validate their integrity and actual capacity. The H2W file contains data generated by H2testw or F3 and is placed on the USB drive or SD card being evaluated in order to test the drive's read + write functionality.

H2W files are generated by H2testw and F3 when a user begins a test and numbered consecutively if more than one H2W file is created (1.h2w, 2.h2w, etc.). H2testw writes H2W files that are 1 gigabyte (GB) in size and that are multiples of 1 megabyte (MB) to fill up a drive or flash card. F3 generates H2W files that fill up the whole space, with each H2W file 1GB in size until the last file, which may be less than 1 GB in order to fill the remaining space. If you encounter an H2W file on a drive you can remove it and delete it. However, if you test it with H2testw or F3 again, another H2W file will be created. To use the H2testw program, insert the USB drive or SD card, open the program, select the target, choose the data volume, then click Write + Verify. Once the test process is finished the program will display information about the read/write speed of the drive and any errors. H2testw was originally developed in German by Harald Bögeholz, but is also available in English. The tool is available for free and only runs in Windows. F3 was developed as an alternative to H2testw that is open source and runs on Windows, macOS, and Linux. It is available for free and is developed as a successor to the H2testw tool.