Also the higher molecular weight helps. Krypton is better than argon; xenon would be better still but is very expensive. Thermal conductivity of gases: https

Also the higher molecular weight helps. Krypton is better than argon; xenon would be better still but is very expensive. Thermal conductivity of gases: https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=907540 https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=90754... Notice how good CFCs are (even though they have plenty of internal degrees of freedom).