Which of the following is not an example of an insulator?
wood
plastic
glass
aluminum foil

So we know that a conductor is a poor insulator since it will absorb the heat and relay it to the environment.  The only good conductor above is Aluminium Foil since it is made of the metal aluminum (metals has a sea of electrons that are able to transfer heat).  As a result the answer is Option 4.

All the others will insulate since they are not able to transfer the heat because of the absence of free electrons.