I imagine that all Americans, at some time or another, have seen an old, worn-out American flag still flying. Invariably, the form of the wear is the same: The red and white stripes have torn apart into separate tatters.
But why is this? A cloth flag wearing into tatters, yes, that’s reasonable. But why are the tears always exactly along the edges of the stripes? If it’s a sewn flag, it would be explained by the seam between the red and white coming apart, but you see this even with the cheap printed flags.
I could understand if it were one color wearing out before the other. Maybe one kind of dye absorbs more UV than the other, or the dye damages the fibers in some other way. But if that were the case, we’d expect to see the tears all within one color, not right on the boundary between the colors.
If flags were rigid objects, I’d attribute it to different thermal expansion, combined with different light absorption or specific heats of the dyes. But it seems hard to justify that for flexible cloth.
I wonder if it could be the printing process - if it’s printed with a block, then the fibres at the edges of any given region of colour could have been subjected to stress and may be minutely fractured, but in such way that only manifests as failure after weathering.
If they’re screenprinted, then I guess it would have to be some differential effect.
Could also be differing rates of deterioriation of the material due to the effects of radiant heat or other solar radiation. The white stripes reflect a lot of the radiation, while the red stripes reflect less and absorb more, leading differing rates of deterioration of the fabric, and possibly, e.g, fractionally different rates of shrinkage, with resulting tears where the two colours meet.
I am not sure that it is true: I have seen some YOUtube videos of tattered flags and while it does look at first as if they are torn along the stripes, this does not bear closer examination.
My WAG is that what you are seeing is an optical illusion.
Back right after 9/11 nine out of ten cars in my area had those cheap car flags on them for several months (including mine). I don’t recall them wearing out that way, the whole end just tattered without regard to the stripes’ positions…
My speculation: After seeing some flags tattered in the way OP describes, or imagining that one has seen such flags, in various “patriotic” contexts (e.g., paintings of that flag that was seen through the dawn’s early light and the rocket’s red glare to be “still there”, or any grunged-up flag recovered from the 9-11 wreckage), I suspect it has been popular to pre-manufacture flags tattered like that, just like manufacturing pre-tattered jeans.
There’s an old flag at my mom’s house right now, that she hasn’t yet gotten around to disposing of. Next time I’m over there, I’ll take pictures. It’s definitely tattered exactly on the stripe boundaries, and it definitely wasn’t made that way deliberately.
But why would that lead to tears where the colors meet, rather than entirely within the weakened color?