Objection 1. It would seem that in hell the damned are tormented by the sole punishment of fire; because Matthew 25:41, where their condemnation is declared, mention is made of fire only, in the words: "Depart from Me, you cursed, into everlasting fire."
Objection 2. Further, even as the punishment of purgatory is due to venial sin, so is the punishment of hell due to mortal sin. Now no other punishment but that of fire is stated to be in purgatory, as appears from the words of 1 Corinthians 3:13: "The fire shall try every man's work, of what sort it is." Therefore neither in hell will there be a punishment other than of fire.
Objection 3. Further, variety of punishment affords a respite, as when one passes from heat to cold. But we can admit no respite in the damned. Therefore there will not be various punishments, but that of fire alone.
On the contrary, It is written (Psalm 10:7): "Fire and brimstone and storms of winds shall be the portion of their cup."
Further, it is written (Job 24:19): "Let him pass from the snow waters to excessive heat."
I answer that, According to Basil (Homilia vi in Hexaemeron and Hom. i in Ps. 38), at the final cleansing of the world, there will be a separation of the elements, whatever is pure and noble remaining above for the glory of the blessed, and whatever is ignoble and sordid being cast down for the punishment of the damned: so that just as every creature will be to the blessed a matter of joy, so will all the elements conduce to the torture of the damned, according to Wisdom 5:21, "the whole world will fight with Him against the unwise." This is also becoming to Divine justice, that whereas they departed from one by sin, and placed their end in material things which are many and various, so should they be tormented in many ways and from many sources.
Reply to Objection 2. It is because fire is most painful, through its abundance of active force, that the name of fire is given to any torment if it be intense.
Reply to Objection 2. The punishment of purgatory is not intended chiefly to torment but to cleanse: wherefore it should be inflicted by fire alone which is above all possessed of cleansing power. But the punishment of the damned is not directed to their cleansing. Consequently the comparison fails.
Reply to Objection 3. The damned will pass from the most intense heat to the most intense cold without this giving them any respite: because they will suffer from external agencies, not by the transmutation of their body from its original natural disposition, and the contrary passion affording a respite by restoring an equable or moderate temperature, as happens now, but by a spiritual action, in the same way as sensible objects act on the senses being perceived by impressing the organ with their forms according to their spiritual and not their material being.
Source: Summa Theologica (New Advent)