Thermal conductivity of glass

ivylim88

Uhmm.. i faced some problem with my experiment of finding the thermal conductivity of glass..i hope that someone can help me.
May i know the extimation of the thermal conductivity of a boiling tube??
isit the same as the thermal conductivity of pyrex glass??
when i want to find the radius of the boiling tube, should i take the reading of the external diameter divided by 2 or the internal diameter divided by 2??
and about the thickness of the boiling tube, its the external diameter deduct the internal diameter then divided by 2 isit??
i will really appreciate your help..