The Webb telescope’s primary mirror is 6.5 meters in diameter, compared with Hubble’s, which is 2.4 meters, giving Webb about seven times as much light-gathering capability and thus the ability to see further into the past.
Another crucial difference is that Webb is equipped with cameras and other instruments sensitive to infrared, or “heat,” radiation. The expansion of the universe causes the light that would normally be in wavelengths that are visible to be shifted to longer infrared wavelengths that are normally invisible to human eyes.
On the other hand, the Hubble telescope is in low Earth orbit, where astronauts could visit and fix things that have broken or worn out, or install new, more powerful instruments on it. Those modifications extended its life years beyond the original estimates.