Format save for Print on Demand

[Carolina Solis]

Hello, 

The size required for a T shirt design in Red Bubble is 2875 x 3900 px. To get that exact size I have read that I have to choose 72 ppi of resolution after doing Export > Export As > PNG (with my Artboard size of 2800 x 3800 px)

In Red Bubble it says: PLEASE also note that DPI and PPI don’t have any effect on your final uploaded image. So that means it is ok to choose 72 ppi? So I did that and bought a sticker with that same design. The design is a bit blurry. Please help.

Now I saved in my computer the same design but with the option "Medium 150 ppi" and the dimensions changes to 4956 x 7120 px and it does look more clear. This format savign process is not clear. 

Then they say too: "A good rule of thumb is that big, high-resolution files make the best prints. Now when we say ‘big’, we're really referring to resolution, not the file’s size. There is a major difference between file size, which is measured in bytes (like megabytes MB) and resolution, which is measured in pixels. When you’re printing work, it’s the pixels that matter. " 

If it is true that it is the pixels that matter then why is blurry when I save it in 2800 x 3800 px in 72 ppi?

[Doug A Roberts · Accepted solution]

A 3-metre wide image that consists of 2800 x 3800 px will look 'blurry'. An A4 page won't.

When they say PPI doesn't matter, it's presumably because they output to one specific (physical, i.e. inches/mm) size, and thus the PPI will be defined by the pixel dimensions of the image you give them.

Of course 4956 x 7120 px will look more 'clear' if you zoom in on it, but it will be massive overkill for the final output size.

[Monika Gause]

Finally they included this advice in their file specifications.

The t-shirt fabric will have a large effect on the result as well. Just send them the pixel dimensions they recommend. They know their machines, the print process and the fabric.