Is glass or plastic a better insulator?

plastic

No. Glass and plastic tend to heat up very quickly and in some cases, plastic may melt if put in extremely hot temperatures. If it does not require boiling something or melting something, I would suggest to use a Styrofoam cup to hold a hot liquid, as it was made for that purpose. Since you can't use Styrofoam, you could use a thermos, which uses a vacuum to insulate the contents. Otherwise, use the glass, it's your best shot.

It depends on the specific glass and the specific plastic, but most glasses has higher heat conductivity than most plastics - so a plastic cup will keep the coffee hot longer.

It is dependent on the thermal barrier that either has, and this is variable depending upon thickness. however glass is a better insulator,where both are the same thickness. It all has to do with the molecular structures, glass molecules are bunch together providing a better trap for BTU's, where plastics have a chain molecule, that are very photon reactive, this is the way plastics biodegrade, and also what makes them poor insulators compared to glass. If you really want to keep your coffee hot longer, try ceramics, they are the suprior insulator.GOOD LUCK !!

Styrofoam will keep coffee hot longer than glass. Plastic cups for coffee are usually styrofoam of some sort.

I prefer the paper cups because I can drink it a little quicker and help the environment.

Glass is only good as an insulator when it comes to blocking electricity.

A plastic is generally much better at insulating against heat that glass.

The structure of plastic molecules (polymers) is random and leads to long paths for heat to transfer through the material whereas glass is a crystalline structure and has many straight paths for heat to transfer through quickly, causing it to rapidly cool off.

If you manufacture it properly you can make something called Aerogel, which is glass but due to it's structure of millions of tiny cells (like a simple piece of cork!) it is a supreme thermal insulator better than any of the plastics so far developed.

well I would say that glass would be a better insulator. This is because back in the old days they used to use glass in thermos's but the problem with glass is that is can shatter if there is a quick change in heat and it needs to be set up with hot water before hand to be most effective. Now a days thermos's have an layer of air (may be vacuume sealed) between the inside and outside of the bottle to insulate.

in my opinion plastic cup is best plastic will get hot with the coffee

and glass will get hot but glass tends to attract exterior temperature and will get cold faster

It would depend on the type of glass and plastic you are talking about.

plastic. You don't want metal or glass because those absorb the heat, taking it away from the coffee. plastic wouldn't absorb it as much.

Definitely plastic, glass transfers heat too well.