What makes Outdoor Poly Outdoorworthy

[poolhound]

OK folks what does outdoor poly have that indoor does not?

Is it something that resists discoloration or does it have to do with ability to withstand the weather?

I am refinishing an item of outdoor furniture and am now out of outdoor poly. I have a surplus of the indoor variety and am considering why I should/not use it.

I dont care about any color issues with the item in question but mainly about protection from the elements. Given the harsh temps we have here I typically end up sanding down and recoating each year anyway so does it really matter?

[cabinetman]

With an oil finish you wouldn't have to sand to recoat, just do a good cleaning. Outdoor oilbase polyurethanes, or spar varnishes, are basically the same but have a higher oil ratio than indoor versions, and have UV additives. The higher oil ratio is to keep the finish somewhat flexible to deal with expansion and contraction. They take a very long time to dry and don't dry hard.
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[LCHIEN]

probably at least, UV filters built in to the formulation to protect the poly and the wood.

[SARGE..g-47]

What Cabinetman said about flexing. Spar will never completely dry or cure as in-door which gives it flex and the reason you should never use it on inside furniture. Frankly I would go get another can to finish. I used in-door on a mail-box once years ago and it had deterioted to the point of stripping down and re-finishing in a little over a year of exposure to the Georgia sun.