Is wearing a flag patch on a backpack against regulations?

Not this again!!!

It is not a flag it is a patch. Flags are officially flags and only come in specific sizes and made of specific materials to be used at specific times and places.

So some insight young pfc. Pick your battles. As 1SG Healy and MSGT below him stated. This is a CSM. You may be right wearing it (and you are right in wearing it sorta, otherwise all that apparel with the flag printed on it would be illegal because it's the flag code, not military regulation that governs this). The fact is flag code is something we as Americans tend to ignore or is bent to different points, the strictest reading makes the flag on your shoulder a nogo.
However right or wrong as he may be in this case. He is a CSM and you are a PFC. This war would be a quick way to a reduction. Don't pick it, comply and move on. If you have a good relationship with him, ie. You're on the BN staff, you could probably get away with letting him know it's the US flag code. But without knowing him, I can't advise that action. And without knowing local policies no one here can advise you on if it is a Garrison thing, or a CSMs personal peeve.

Bottom line up front, just execute the directive, learn from it and live to become the CSM you want to be.

Uniformity is the Army way. However, placing the American Flag on one's rucksack is not against regulations, unless there is an amendment. This is in garrison. In enemy territory, having an American Flag on your rucksack can make you the target of enemy fire. Best is to remain in uniform with the unit or the Army standard.

Just to add one more thing into the mix: what is a flag? Even in the US Code it says the patch is a “replica”. So does a replica get the same respect? If so, then how can you wear it on your sleeve and crawl in mud and such?

I believe that (in simple terms) a flag is a two sided cloth (cotton or synthetic) that is designed to be displayed from a staff or pole and that flag replicas that are printed for other purposes are not flags and don’t require the same attention (though they should be treated respectfully).

Your not gonna find anything about a flag patch, not a actual 2 sided flag being on a privately owned backpack in any regulation or US flag code. If your that anal rentitive about it, then you need to direct that concern to whether your troop with that backpack can actually hit something with their assigned weapon when the time arises.

In a perfect world, I'd say, "well no, it is not against regulation."
However, i reality, PFC. Parker, there are different variants of "backpacks". Ruck sack, assault pack, etc, ect. If you mount a flag on CIF issue, then you can be charged with destruction of property and subject to charges in this reguard. However against regulations, AR 670-1 isn't clear about whether or not it is regulation. However, it is called attention to detail, and attention to uniformity. Additionally, your unit may have special orders or needs for such SOP; Some units wear IR Id's on thier kits to identify themselves to friendlies. But hell, on a backpack? It is a go all day.

The regulation only covers commercial logos on backpacks. So as long as the flag is being displayed properly it should be fine. I had the Maryland flag on my bag for a while and any time I was bothered about it I politely explained that the flag isn’t a commercial logo and I was left alone. Now, I will say sometimes it’s not a hill worth dying on and you’re better off saying, Rgr and moving on.

I’m just a lowly SPC, but on my backpack I have a flag facing what people would consider the normal way, and it is coyote to match the backpack as well. So this flag could never be warn on a uniform it is simply a moral patch.

In my day we never had flag patches on our uniforms or Alice packs, I had a MACV patch and rank under my collar. That was it.