Okay, here goes. I have a 72 Strat with enough poly for ten guitars. The necks not bad but the body's thick. I bought a new Gibson LP Studio 60's Tribute that seems like the nitro's so thin that it seems like it was sprayed from across the room. The Gibby is more resonant, but I think it's more because the body's chambered. I think the whole finish thing is a crock. The only good thing is I think the Gibson will show some nice wear pretty quickly while my Strat even though it has a couple of chips still shines pretty well.

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Life...... It's sexually transmitted and always fatal

. . . and the poly finish tends to hold up MUCH better when you spill a beer or two on it!!

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"It's about sound and sound alone. Looks are irrelevant. You can have the best-looking guitar on earth, but if the sound isn't there it is nothing more than a beautiful piece of trash. The sound it makes is the soul of any guitar."

Haa!,yep it's almost indestructable.....the perfect barroom guitar finish.

The immature and likely unemployed musicians don't get it. Your top professionals don't miss the performance, particularly the top side musicians. Otherwise they wouldn't understand there place in the music.

How true. But even professionals like inspiring tools. Kinda like somebody likes P-Basses with old broken in flats and the other person likes a Jazz Bass with round-wounds. The sound will be different, but the music will only be as good as the artist working it.

Just because I have (I don't) a master mechanics tool bench, I still can't rebuild an engine.

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Back to the original question. When NEW both will sound the same. The nitro is breathable, only so long as there is not a poly undercoating and more often than not there is a poly sealer/primer even on instruments touted as being nitro finished. If the finish is all nitro though, since it is breathable moisture will continue to escape in trace amounts from the wood resulting not only in slightly lighter weight but also less density which can enhance the body's resonance over the passing of decades.

The fact they were all nitro is one reason why original Pre-CBS instruments (actually '63 and back) are so desirable today tone wise. So an instrument with a poly finish or undercoat will always have the same or practically the same moisture content. A very tiny amount of moisture can vent from screw holes, cavities, neck joints and switch slots on a poly finished instrument, but this venting is negligible compared to a porous all nitro finish.

People often forget that an all nitro finish isn't just porous one way, so when an instrument is stored or used in high humidity environs it can actually absorb moisture over an extended period of time. As previously mentioned Poly is far more durable and better all around for longevity on guitars. I'll never be able to afford a true vintage all nitro Fender, so I look for one that sounds good off the rack in the first place.

Additionally applying wax or sealers to an all nitro finish will slow the gradual drying of the wood.

There it is. Nitro is going to be affected by humidity. Humidity is pretty much everywhere except the Antarctic.