What polymer material is JWST's sunshield made of?

The polymer material used for JWST’s sunshield is Kapton. More precisely, its five membranes are made from Kapton E, a polyimide film chosen for its strength and stability in the extreme environment of space.

The sunshield is designed to block light and heat from the Sun, Earth, and Moon. JWST observes infrared light, so its telescope and instruments must remain extremely cold; the shield passively cools the observatory to roughly 40 kelvin. Its five layers are coated with aluminum, while the outer layers also receive a doped-silicon coating to improve thermal performance and durability.

Kapton is not the same as the reflective coating. The underlying polymer is Kapton, while aluminum and silicon coatings help reflect sunlight and radiate heat away. This distinction causes occasional confusion with materials such as Mylar, another reflective plastic film.

The shield is roughly tennis-court-sized when deployed but had to be folded inside the Ariane 5 rocket. Its deployment was completed on January 4, 2022, after launch.