From Giant in the Playground Forum:
Well a Great Wyrm Red breathes hot enough to theoretically
liquify[melt] 4 inches of solid iron across an 80 foot or so line. So an 80 foot wall of iron 4 inches thick could beliquified[melted] by a single attack by a Great Wyrm Red.
the end result is that the air breathed out by the dragon [onto the iron reaches] 1520 degrees Kelvin, 1246 degrees Celsius, or 2276 degrees Fahrenheit.
Can an umbrella be used to deflect a breath from the dragon, and also keep its average human user alive?
If so, what materials would it have to be made of? It must still be light enough for an average person to still raise.
Assume the umbrella is a small personal umbrella, with at most 60cm radius, with a surface area of roughly 2.25-2.5 meters squared.
This happens in a low-fantasy world, with some magic, but still has similar physics.
Edit: to better support yes answers, seeing as the d&d dragon’s breath is far more deadly than expected, you can assume the umbrella can activate magic, but only to turn the umbrella into a sphere/semi-sphere around the user.
Edit2: Due to an error made in calculations by the source on the temperature of the breath, we now have some inconsistencies for temperatures mentioned in some answers. We will assume 1246 degrees Celsius for this question (enough to melt ductile and cast iron), as all of the answers mentioning higher temperatures of 1500 degrees scale linearly, so this does not invalidate any of the premises.