How many layers does JWST's sunshield have?

The James Webb Space Telescope’s sunshield has five layers. The membranes are arranged with carefully controlled gaps so that heat radiates outward instead of passing directly from the hot side to the telescope.

Webb observes infrared light, so its mirrors and instruments must remain extremely cold. The sunshield blocks heat and light from the Sun, Earth, and Moon while keeping the telescope in permanent shade. Its five layers separate the spacecraft’s warm side from its cold side and help reduce solar heating by roughly a factor of one million.

Each membrane is made from Kapton, a lightweight, heat-resistant polyimide film. The layers are coated with reflective materials, including aluminum; the sun-facing sides of the two hottest layers also have a treated-silicon coating. The largest outer layer faces the Sun, while the innermost layer is closest to Webb’s optics.

The shield is about the size of a tennis court when fully deployed, yet it had to be folded inside the Ariane 5 rocket’s nose cone. Engineers studied designs ranging from two to seven layers and chose five as the best balance of cooling performance, redundancy, weight, and mechanical complexity.