Seen from a tanker’s boom, the pilot of an F-22 Raptor appears to sit beneath a sheet of gold leaf. The colour is not paint, and it is not a sun visor. It is an electrically conductive film on the canopy, thin enough to see through, and its job is to stop radar energy at the glass before it reaches the cockpit.

The cockpit is the problem. To a radar it is a cavity full of complex shapes: the ejection seat, the instrument panel and the pilot’s helmet, which alone can form a sizeable return. A transparent conductor on the canopy, vapour-deposited gold or indium tin oxide (ITO) in most published accounts, presents the radar with a controlled shape instead and deflects the incoming waves away from it.

The idea runs from the ancestors of the F-117 Nighthawk au F-35 Lightning II. It explains the F-16’s Have Glass programme, the Raptor’s gold canopy and why one F-35 canopy that strayed to Hong Kong this year drew so much attention. The film is not a free upgrade, though: it costs light, it wears, and it must be maintained like the rest of a stealth skin.

Why a cockpit glows on radar

Plastics are poor radar reflectors, which is why radomes are made of them. Canopy acrylic and polycarbonate behave the same way: to a radar an untreated canopy is barely there, and beneath it lies a compartment packed with edges and equipment. That makes the cockpit a radar trap: waves enter, bounce between the objects inside and come back as a stronger return.

The cure relies on a principle familiar from chaff: even a very thin layer of metal makes a surface strongly reflective to radar. Coat the canopy with a conductor and the radar meets a smooth, controlled shape rather than the clutter beneath it. Designers can then decide where the reflected energy goes, and on a stealth fighter that means away from the transmitter.

Two materials are usually named. One is gold, laid down as a vapour-deposited film. The other, ITO, is a transparent conducting oxide: colourless in thin layers yet electrically conductive, and a thin film can pass more than 80 per cent of visible light. A Mitsubishi Heavy Industries patent application, published in Europe in 2005, describes windows for stealth aircraft carrying “a transparent conducting film such as gold or ITO”, which provide both radar stealth and a shield against harmful electromagnetic waves other than visible light.

Sandboxx explains the stealth technology behind tinted fighter canopies.

The film can earn its keep in other ways. ITO is widely used for infrared-reflecting coatings, and accounts of the F-22 credit its canopy layer with reflecting infrared as well as handling radar. PPG, a supplier of military transparencies, makes conductive coatings for applications ranging “from low observables and electrical heating to solar infrared, ultraviolet, night vision, and laser protection”.

F-117: flat glass, faceted like the rest

The idea predates the F-22. Have Blue, the demonstrator that first flew in December 1977 and led to the F-117, is described as carrying radar-absorbent material on its flat surfaces and special coatings that gave its windscreen metallic characteristics. The production F-117 carried the faceting into the cockpit: its canopy is a cluster of flat panels, and the pilots accepted what that did to the view.

Lockheed test pilot Hal Farley, who made the first F-117 flight, remembered a canopy warning light on that sortie as troubling “because the canopy is also the windscreen”. Keeping the jet’s skin stealthy was a craft of its own: Lt. Col. Todd Flesch said pilots “quite literally placed our lives” in the hands of the maintainers who kept up its low-observable materials.

One F-117 canopy is now a museum exhibit. The canopy of 82-0806, shot down over Serbia on 27 March 1999, is displayed at the Museum of Aviation in Belgrade, its flat panels and saw-tooth edges plain to see. Its pilot, Lt. Col. Dale Zelko, ejected and was rescued.

Have Glass: the F-16 goes gold

The F-16 had its signature reduced piece by piece. On the Block 30/32, F-16.net notes, the engine inlet, always a major contributor to the jet’s radar cross-section, was treated with several radar-absorbing coatings. The canopy was tackled under the US Air Force’s Have Glass programme, which according to Sandboxx came in stages. The first applied a thin ITO layer to the canopy, deflecting radar instead of letting it through to reflect off the pilot’s helmet and the visible parts of the ejection seat.

The second stage added radar-absorbent material to parts of the airframe. Sandboxx puts the combined cut in the F-16’s overall radar return at as much as 15 per cent. Have Glass is also the name of the paint: the standard two-tone grey is a radar-absorbing finish containing microscopic metal grains.

Have Glass V, a darker overall grey in the FS36170 shade also used on the F-35, appeared in 2012 on the Block 50 F-16CMs of US units flying suppression of enemy air defences, and has since spread to other squadrons. Have Glass has travelled abroad too. The 34 F-16s Italy leased under a 2001 deal were repainted with Have Glass paint at Hill Air Force Base before delivery, Denmark began repainting its fleet in Have Glass grey in 2020, and Argentina unveiled its first F-16 in a dark grey Have Glass scheme in 2024.

F-22: one bubble, no bow

On the Raptor, stealth was part of the canopy specification. Its transparency, made by Sierracin, has been described as the largest piece of polycarbonate formed in the world, with no canopy bow, top-grade ‘Zone 1’ optics throughout and the “requisite stealth features”. The complete canopy measures about 140 by 45 by 27 inches (355 by 115 by 69 cm) and weighs roughly 360 lb (163 kg).

The 3/4-inch (19 mm) transparency is made from two 3/8-inch (9.5 mm) polycarbonate sheets, heated and fusion bonded into one piece, then drape forged. It was tested against a 4 lb (1.8 kg) bird at 350 knots (about 650 km/h) and protects the pilot from lightning. To close, the canopy comes down, slides forward and locks in place with pins.

The gold is the coating. Published accounts of the Raptor, Bill Sweetman’s 1998 history among them, attribute the tint to an indium tin oxide layer that handles radar and also reflects infrared. Thin conductive films produce interference colours as well, which helps explain why F-22 canopies in official photographs range from gold to copper-orange.

Durability was an early weak point. In testing, the Pentagon’s Director, Operational Test and Evaluation found the cockpit canopy falling far short of its service-life requirement, and the canopy was redesigned.

F-35: a coating that has to be kept

The F-35 changed the layout. Lockheed Martin’s Code One magazine notes that the X-35 demonstrator had a two-piece, side-opening canopy with a conventional bow frame, while the F-35 has a one-piece, forward-opening canopy with an integrated bow frame, a change that improved signature characteristics while keeping weight down. The transparency is stretched acrylic, made by Lockheed Martin’s subcontractor GKN Aerospace.

Its optics are checked canopy by canopy. As Code One described in 2011, every F-35 canopy goes through a mapping laboratory at Fort Worth before installation, because each one distorts the view in its own way. The measurements become look-up tables that the avionics use to correct what the head-up and helmet-mounted displays show, so a replacement canopy needs its own table. Mike Jones, the Lockheed Martin Technical Fellow who invented the mapper, sums up the problem.

What is inside the F-35’s film has not been published. Sandboxx, reading GKN patent filings that have not been officially tied to the jet, suggests a thin gold layer sandwiched between layers of aluminium-doped zinc oxide. The US Air Force says the canopy’s outer surface is part of the jet’s stealth, or low-observable, capabilities. In some light it shows a distinct yellowish tint.

Keeping that surface intact has been the hard part. In 2019 the F-35 Joint Program Office named canopies and spare parts as the major drivers in its push for an 80 per cent mission-capable rate, and its spokeswoman explained the canopy problem to Breaking Defense.

From a sealant change to a Hong Kong detour

Recent findings, the F-35 Joint Program Office said, pointed to a mundane cause: a change to the sealant between the transparency and the frame, introduced in 2015 as a cost-saving measure. Canopies with the correct sealant followed. In March 2020 a canopy from a second manufacturer passed its final ejection-seat test at Holloman’s high-speed test track, heated to 200°F (93°C) to simulate a hot day; the office had named PPG as the second source it was qualifying. In April 2025 the 388th Fighter Wing at Hill Air Force Base began fitting new, more durable canopies.

The canopy’s place in the F-35’s signature is why one unserviceable example made headlines in September. Politico reported on 18 September 2026 that F-35 components shipped from Australia for the United States, a canopy among them, had ended up in Hong Kong. The Joint Program Office said it was working to retrieve them; Australia’s defence minister, Richard Marles, said they were not sensitive parts. A canopy alone cannot reveal the secrets of the whole F-35, but Sandboxx points to the coating as what makes it worth studying.

Why not every fighter is gold

If the film works, why do so many fighters fly with clear canopies? The first reason is light. The Mitsubishi patent spells out the trade-off: the better a film shields against radar, the less visible light it passes, and adequate performance can push transmission down to 70 per cent or lower, darkening the pilot’s view. Strongly curved canopies also make a film of uniform thickness hard to apply.

The second is durability. A ceramic film such as ITO does not deform with a canopy flexing under changes in pressure and temperature, and can crack, which is why the same patent notes it is applied to the inner side, where the canopy deforms less. The F-35 shows what an exposed coating demands: inspection, repair and, at Eglin Air Force Base, a purpose-made cover that maintainers designed to protect it.

The third is return on the effort. On a fighter that was not shaped for stealth, the canopy is one reflector among many, and Sandboxx’s estimate for Have Glass stages I and II together is a reduction of up to 15 per cent. The same transparency may also need its own coatings for heating, solar protection, night vision or lasers.

On a stealth fighter the calculation changes. The US Air Force counts the F-35’s canopy surface as part of its low-observable signature, and the Raptor’s canopy came with stealth features built in. The gold film is how designers keep a radar out of the busiest space on board without taking away the pilot’s view. The pilot still sees out. The radar, ideally, does not see in.

Sources: Code One (Lockheed Martin), 15 May 2008, 22 June 2011 and 24 August 2015; Breaking Defense, 23 July 2019; U.S. Air Force via DVIDS, 10 April 2020, 7 December 2023 and 10 April 2025; Hill Air Force Base, 29 October 2019; GlobalSecurity.org, F-22 Raptor cockpit; Mitsubishi Heavy Industries, European patent application EP1520842A1, 6 April 2005; PPG Aerospace, military aviation transparencies; Sandboxx, 12 December 2022 and 28 September 2026; X post by Audrey Decker (Politico), 18 September 2026; The Aviationist, 19 September 2008, 30 August 2012, 25 September 2016, 15 October 2020, 28 April 2021, 16 April 2024, 22 September 2026 and 24 September 2026; F-16.net, F-16C/D Block 30/32; U.S. Department of Defense photograph via U.S. National Archives, 26 February 1998; Wikipedia: Stealth technology, Radar cross section, Indium tin oxide, Lockheed Martin F-22 Raptor, Lockheed F-117 Nighthawk, Lockheed Have Blue, 1999 F-117A shootdown