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Is there any reason to believe that a fiberglass sousaphone would be easier to tune in changing temperatures than a brass sous/tuba?
I'll be playing about 35 evening concerts this summer outside. As you all know tuning can be quite challenging outside when temperatures fall, especially when the tuba cools off during long rests. I was wondering if a fiberglass instrument would be less susceptible to temperature changes (or have I got the science of this all mixed up?)

I don't feel a fiberglass horn will offer any advantage over a brass horn in terms of staying in tune. The advantages I see are as follows: lighter weight, less chance for corrosion, and a fiberglass horn will not "check" the lacquer finish when brought into a warm environment when it's cold. This causes the lacquer to crack and check due to the lacquer expanding at a slower rate than the brass. Guitars will do the same thing, and as a rule of thumb, if you expose your horn to a warm environment and the finish "fogs up", quickly put it back in its case and allow it to come up to room temperature slowly to prevent finish checking.

Thanks,
The cold air column is what makes our tuning go flat in cold temperatures. I was wondering if fiberglass might help to keep the air column warmer longer because it's a better insulation material than brass.
It's all theory. I was wondering if anyone had ever experienced this first hand, (even though the first part of the sousaphone is still brass)

Re: Firsthand experience:
For one year, my Junior year at NCSU (Raleigh, NC), we had a mix of old King and Conn fiberglass sousas (bought in the '60s) and a few new Conn 20K (with satin silver finish) instruments. I can confirm that they experienced similar tuning issues on both kinds of instrument when the weather changed, though we never really got cold here during football season that year. Before that year, the section was all fiberglass. For my senior year, we were all on 20Ks.

One thing to note - I think the brass sousas (in this case, satin silver) warmed up faster in the sun and cooled off faster in the shade than our white fiberglass / laquer brass sousas did. At the very least, that's how it felt to my fingers. I will not say that it was enough to affect tuning though.

From a materials perspective, it also looks like brass has a lower thermal expansion coefficient (expansion/contraction due to temperature change) than epoxy/fiberglass.

http://www.engineeringtoolbox.com/linea ... -d_95.html