John J.
Senior Member.
Weather balloons are typically latex due to elasticity and burst resistance.
Specular highlight suggests a metallic sphere, such as metal-coated mylar.
The Mosul sphere looks metallic, like e.g. a metalized Mylar party balloon:
But so do these Second World War balloons, which predate BoPET by over a decade:
Top photo courtesy of Alamy stock image website; a balloon used by a German artillery battalion, 1940.
Lower photo, balloons to deliver propaganda leaflets.
There's been a bit of balloon-spotting and various theories involving balloons in the threads
Silver Orbs reported over Berlin in WWII, and
Middle East 2022 MQ-9 Observed Apparent Spherical UAP (via AARO)
where this image was posted by @deirdre,
Aleppo is in Syria, but we've seen that Mylar party balloons were available in Iraq, even during troubled times.
Equally, I wonder if we're making a mistake in assuming the Mosul sphere, if it is a balloon, is a Mylar balloon.
The WW2 photos seem to show that pre-BoPET balloons, probably latex, can appear to be reflective and have bright spots in the right lighting conditions.
Maybe Iraqi (pro-government) artillery used balloons.