What Is a PART File?
A .part file showed up where your download should be. It is an unfinished download. Here is how to finish it, and when it is safe to just delete it.
What a PART file is
A .part file is an incomplete download. Firefox and many download managers (like JDownloader or wget) write incoming data to a temporary file with .part added to the real name — for example movie.mp4.part — and only rename it to movie.mp4 once every byte has arrived.
Why it is left behind
A leftover .part file means the download did not finish: the connection dropped, you closed the browser, or you cancelled it. The bytes already downloaded are stored, but the file is not complete and usually cannot be opened.
How to finish it
In Firefox, open the Downloads panel (Ctrl+J) and click the resume (retry) button next to the interrupted item — Firefox keeps filling the same .part file. If it is gone from the list, download the file again from its source. A download manager usually has its own Resume button that continues the existing .part.
Is it safe to delete?
Yes, once you have abandoned that download. Deleting the .part only throws away the incomplete data. Do not delete one that is still downloading.
Can partial data be recovered?
Sometimes. For plain media like a large video, some of the already-downloaded portion may play if you rename a mostly-complete .part to the real extension — but the file will be truncated and often will not open at all. Resuming the download is always the reliable fix.
FAQ
Can I open a .part file?
Usually not — it is only a portion of the real file. Resume or restart the download to get a complete, openable file.
Is it safe to delete a .part file?
Yes if the download is finished, dead, or cancelled; you only lose incomplete data. Do not delete one that is still downloading.
What program makes .part files?
Firefox names in-progress downloads with .part, and so do many download managers such as JDownloader and wget. Chrome uses .crdownload for the same thing.
Can I recover a partial download from a .part file?
Occasionally a large media file will partially play if renamed, but it is truncated and often unopenable. Resuming or restarting the download is the reliable option.