Memory of mapped files in PHP, what is the difference between php: // temp and php: // memory

I need a way to store a file in memory very briefly in PHP, the file is created and then sent directly to another web service. I see that streams php://tempand are available with PHP 5.1 php://memory, but there is not much difference between them: it php://tempsupports the function stream_select()and php://memorydoes not. Which one should I use in this case, or is there a better way to make memory mapped files in PHP?