Why the artwork moves
Tins are printed on a flat sheet and drawn into shape after. Wherever the metal has to travel to make a shoulder or a corner radius, it stretches, and everything printed there stretches too.
A circle goes oval on the shoulder. Type thins where the draw is deepest. How much depends on how far the metal moves at that exact point, so it varies across one tin and again across every size in a format.
What we do about it
You get a dieline for the size you picked, with the drawn areas mapped, so your designer places artwork against the real distortion instead of a flat rectangle. The compensation happens before anything goes to plate.
None of this is judgeable on screen. Left alone it turns up at proof, which is late and expensive to fix.
What to send
Vector files where possible, with fonts outlined and Pantone references named rather than described. Photographs at 300dpi at final size.
If you have no designer, send whatever you have. That work is done here, and you get the files afterwards whether or not you order again.
Four things that save a round of proofing
Keep critical type off the deepest draw areas. Give logos breathing room from corner radii. Do not put a fine hairline rule right at a shoulder. And decide early whether a colour is Pantone or CMYK, because it changes how the file is built.
None of these are rules you have to know in advance. They are on the dieline. But knowing them while you design saves a cycle.
Hold one before
you specify it.
Tell us what you're packing and we'll send the formats that suit it.