"Tin canning" describes the longitudinal ridges which often appear in low density LDPE polyethylene film - usually blown PE film.
For many applications of PE film, tin canning does not matter. Heat shrink film is one example. The ridges smooth out when the film shrinks. Same goes for industrial box liners. Not so for film which gets printed, laminated or coated. These demanding processes require a perfectly smooth " lay flat" film. Any film with a slight indication of tin canning ( usually by the pressman who taps at points across the roll looking for a slight marshmallow like surface ) gets rejected before it gets put on the press, laminator or coater.
Of course only the blown film manufacturers care about the causes of tin canning. Customers just want flat PE film. If you're interested, here are some factors which can contribute to tin canning:
a no slip / antiblock only film with a high COF
will not "settle" after being wound up
thinner films will get stretched more on the way to the winder, exacerbating any imperfections in gauge profile
treated films with their higher surface energy tug at the interfaces of the layers on the roll
wider webs have more area across the web
While the main culprit is excessive winding tension which stretches the film and does not trap microscopic pockets of air in the roll, you might have to live with occasional tin canning if you call out a no slip, wide, treated PE film.