Looks like an over layer with blend mode or half-opacity and a mesh pattern effect applied to it.
It is very simple to create a pattern. Just create a small image that could be repeated in all sides. Than select the area you want to repeat over the image.
Than go to "edit" in main menu bar and click on "Define Pattern". That pattern can be used any where than.
You can do one more thing. Search for the same pattern on google if you find any image than again follow the same steps I had written above.