To make observations in the infrared spectrum, the JWST must be kept under 50 K (−220 °C; −370 °F) otherwise infrared radiation from the telescope itself would overwhelm its instruments.
It therefore uses a large sunshield to block light and heat from the Sun, Earth, and Moon, and its position near the Earth–Sun L₂ point keeps all three bodies on the same side of the spacecraft at all times.
Its halo orbit around L₂ avoids the shadow of the Earth and Moon, maintaining a constant environment for the sunshield and solar arrays.
The shielding maintains a stable temperature throughout the structures on the dark side, which is critical to maintaining precise alignment of the primary mirror segments.

The five-layer sunshield, each layer as thin as a human hair, is constructed from Kapton E, a commercially available polyimide film from DuPont, with membranes specially coated with aluminium on both sides and doped silicon on the Sun-facing side of the two hottest layers to reflect the Sun's heat back into space.
Accidental tears of the delicate film structure during testing in 2018 were among the factors delaying the project.

The sunshield is designed to be folded twelve times so that it will fit within the Ariane 5 rocket's (4.57 m × 16.19 m) payload fairing.
Once deployed at the L2 point, it will unfold to 14.162 × 21.197 m. The sunshield was hand-assembled at ManTech (NeXolve) in Huntsville, Alabama, before it was delivered to Northrop Grumman in Redondo Beach, California for testing.
To make observations in the infrared spectrum, the JWST must be kept under 50 K (−220 °C; −370 °F) otherwise infrared radiation from the telescope itself would overwhelm its instruments. It therefore uses a large sunshield to block light and heat from the Sun, Earth, and Moon, and its position near the Earth–Sun L₂ point keeps all three bodies on the same side of the spacecraft at all times. Its halo orbit around L₂ avoids the shadow of the Earth and Moon, maintaining a constant environment for the sunshield and solar arrays. The shielding maintains a stable temperature throughout the structures on the dark side, which is critical to maintaining precise alignment of the primary mirror segments.
The five-layer sunshield, each layer as thin as a human hair, is constructed from Kapton E, a commercially available polyimide film from DuPont, with membranes specially coated with aluminium on both sides and doped silicon on the Sun-facing side of the two hottest layers to reflect the Sun's heat back into space. Accidental tears of the delicate film structure during testing in 2018 were among the factors delaying the project.
The sunshield is designed to be folded twelve times so that it will fit within the Ariane 5 rocket's (4.57 m × 16.19 m) payload fairing. Once deployed at the L2 point, it will unfold to 14.162 × 21.197 m. The sunshield was hand-assembled at ManTech (NeXolve) in Huntsville, Alabama, before it was delivered to Northrop Grumman in Redondo Beach, California for testing.
James Webb Space Telescope