Glass Capacitor: High Reliability Applications, Specs, and Selection Guide

There’s a subset of component selection decisions in PCB design where “good enough” genuinely isn’t an option. Missile guidance electronics, satellite transponders, downhole oil-well telemetry, implantable medical devices — in these environments, a component failure isn’t a warranty claim, it’s a mission abort or worse. For the small-value, precision capacitor position in these designs, the glass capacitor has been the answer for more than fifty years, and it remains the answer today.

If you’ve only ever worked in consumer electronics or commercial industrial PCB design, you may never have touched one. They’re expensive, physically larger than ceramic equivalents, and stocked by specialist distributors rather than mainstream electronics chains. But if your work ever crosses into aerospace, defense, space, or high-reliability medical electronics, understanding the glass capacitor thoroughly is not optional. This guide covers everything you need to know.

What Is a Glass Capacitor?

A glass capacitor is a fixed capacitor that uses glass as its dielectric material. The construction is a fused, monolithic stack of alternating glass layers and metal electrode layers — typically aluminum or precious metal — fired and fused at high temperature into a hermetically sealed, solid body. The leads are sintered directly into the glass body, not crimped or soldered externally, giving the entire assembly a single-material integrity that no other capacitor construction method replicates.

Glass dielectric capacitors have been an engineer’s first choice for applications that require a capacitor that will provide extreme long-term stability and reliability for over fifty years. That’s not marketing language — it’s a straightforward statement about a dielectric material whose properties simply don’t change with time, temperature, or radiation in the way that polymer or ceramic dielectrics do.

Few materials possess the characteristics of glass. Glass does not corrode or degrade. Glass is not subject to microfractures or delaminations. Hermetically sealed glass capacitors are almost immune to severe environmental effects such as shock, vibration, radiation, resistance, moisture, salt spray and solder heat.

For a PCB engineer specifying components for a ground-based commercial product, those properties might sound like expensive overkill. For anyone designing a satellite that will spend fifteen years in low Earth orbit with no possibility of service, they’re exactly what the job demands.

Glass Capacitor Construction and How It Works

The Fused Monolithic Structure

Unlike multilayer ceramic capacitors (MLCCs), which are sintered ceramic with metal electrodes fired together but remaining distinct material phases, a glass capacitor is truly fused — the glass dielectric and metal electrodes become a unified monolithic structure during the manufacturing process.

The process starts with thin glass tape, alternated with metal electrode layers, pressed into a multilayer stack and then fired at high temperature. The glass softens and fuses around and through the electrode layers, creating a hermetically sealed body with no internal air voids, no adhesive interfaces, and no mechanical joints that could shift or delaminate. Wire leads are fused into the end faces of the body, not attached afterward.

Fused monolithic construction provides excellent electrical performance, environmental immunity, stability, and retraceability.

The word “retraceability” in that context is important. It means the capacitance-versus-temperature characteristic follows the same curve repeatedly, cycle after cycle, with no hysteresis. You can cool a glass capacitor to -75°C, warm it to +200°C, return it to room temperature, and the capacitance value returns to exactly where it started. This is not the behavior of ceramic Class 2 dielectrics, and it’s one of the glass capacitor’s most practically important properties for precision circuit design.

Glass-K: The Low-Noise Variant

Beyond the standard glass dielectric CY series, there is a Glass-K variant. CK Series Glass-K capacitors offer low noise and low dielectric absorption rate (less than 0.1%), for digital systems and sensor applications where low loss and stability are required.

Dielectric absorption — sometimes called “voltage soakage” — is a phenomenon where a capacitor, after being discharged, partially recharges itself from residual polarization in the dielectric. In high-precision ADC circuits, sample-and-hold amplifiers, and precision integrators, dielectric absorption is a real error source. Glass-K’s sub-0.1% absorption is among the lowest of any capacitor technology.

Key Electrical Specifications of Glass Capacitors

Capacitance values range from 0.5 pF to 10,000 pF with tolerances to ±0.5%. Rated voltage is from 50 to 2,000 VDC, with a temperature coefficient of 140±25 ppm/°C. Operating temperature range is -75°C to +200°C.

Parameter	Typical Value	Notes
Capacitance Range	0.5 pF – 10,000 pF	CY series; Glass-K similar range
Voltage Rating	50V – 2,000V DC	Derate per MIL-PRF specs
Tolerance	±0.5% to ±5%	Much tighter than ceramic Class 2
Temperature Coefficient	140 ± 25 ppm/°C	Linear, repeatable, no hysteresis
Operating Temperature	-75°C to +200°C	Exceptional upper limit
Dissipation Factor	< 0.1%	Extremely low loss
Q Factor	Very High	Excellent for RF resonant circuits
Dielectric Absorption	< 0.1% (Glass-K)	Critical for precision analog
Insulation Resistance	> 10,000 MΩ	Exceptional leakage control
Aging Rate	Zero	Unlike NPO ceramics, truly zero

The zero aging rate deserves emphasis. Class 1 NPO/C0G ceramic capacitors are specified as having negligible aging, but there is a slight crystalline relaxation effect in ceramic dielectrics over time. Glass, being an amorphous solid rather than a crystalline material, has no crystalline grain structure to relax. The capacitance of a glass capacitor measured in 1975 and measured again in 2025 on the same part will be the same, within measurement uncertainty. That’s a remarkable property for a passive component.

Military Specifications Governing Glass Capacitors

Understanding the MIL-PRF landscape is essential if you’re buying glass capacitors for defense or aerospace work. Specifying the part correctly means referencing the right document.

Specification	Coverage	Reliability Level
MIL-PRF-23269	Established reliability glass dielectric	S, R, P, M levels
MIL-C-11272	General-purpose glass dielectric (legacy, superseded)	Commercial/military
MIL-PRF-11015	Glass composition (Glass-K) established reliability	S, R, P levels
MIL-PRF-39014	Glass composition chip capacitors	QPL controlled
NASA EEE-INST-002	Derating and screening for space applications	Space grade
ESCC 3009	European Space Agency qualification	Space grade (ESA)

MIL-PRF-23269F covers the general requirements for established reliability, glass dielectric, fixed capacitors. Capacitors covered by this specification have failure rate levels established in accordance with MIL-STD-690, established at a 90 percent confidence level and maintained at a 10 percent producer’s risk, based on life tests performed with rated voltage applied at 125°C.

The “established reliability” (ER) designation means the manufacturer has demonstrated a quantified failure rate — expressed in failures per million hours — through extended life testing under controlled conditions. This is fundamentally different from selecting a commercial part and hoping it’s reliable. ER qualification gives you a documented failure rate you can plug into system reliability calculations (MIL-HDBK-217 or similar).

Reliability levels under MIL-PRF-23269 are designated S (space, most stringent), R, P, and M (military, least stringent of the four). This style of capacitor is used in aerospace, military and satellite applications which require “S” level reliability, radiation hardness and operating temperatures up to 200°C.

High Reliability Applications of Glass Capacitors

Aerospace and Military RF Systems

Glass capacitors are used in RF circuits where ultimate performance is required. They offer a low temperature coefficient with no hysteresis, zero aging rate, no piezo-electric noise, zero aging rate, and extremely low loss. They also have a large RF current capability, with high operating temperatures, often up to 200°C.

In military radar systems, electronic warfare platforms, and airborne communication equipment, the resonant circuits that determine filter and oscillator frequencies must hold their values across altitude (temperature) changes, vibration, and decades of service life. A glass capacitor in the resonant tank of a VCO or bandpass filter contributes negligibly to frequency drift compared to virtually any other dielectric choice.

Satellite and Space Electronics

Space is the most demanding environment electronics will ever face: wide temperature swings (from deep cold in shadow to extreme heat in direct sun), ionizing radiation that degrades most dielectric materials, zero possibility of maintenance, and mission durations measured in decades. The unique materials and construction techniques involved with glass capacitors make them ideal for use in radiation environments.

Most polymeric dielectric materials degrade under ionizing radiation — the long-chain molecular structure is disrupted by particle impacts, leading to changes in dielectric constant, increased leakage, and ultimately breakdown. Glass, being an inorganic oxide network, is inherently radiation-hard. Its dielectric properties under space radiation loads are far more stable than any plastic film or organic dielectric.

Missile Guidance and Weapons Systems

Precision guidance electronics require components that maintain exact parameter values under high shock and vibration loading. A glass capacitor’s fused monolithic construction has no interfaces to delaminate, no leads to fatigue, and no internal voids to collapse under acceleration. Hermetically sealed glass capacitors are almost immune to severe environmental effects such as shock, vibration, radiation, resistance, moisture, salt spray and solder heat.

Medical Implantable Devices

Implantable cardiac defibrillators, neurostimulators, and cochlear implant controllers operate inside the human body at 37°C continuously, need to last 10–15 years without service, and cannot under any circumstances fail in a way that harms the patient. The combination of hermetic sealing, zero aging, and exceptionally high insulation resistance makes glass capacitors appropriate for precision timing and signal conditioning functions in these devices.

Downhole Oil and Gas Electronics

Measurement-while-drilling (MWD) and logging-while-drilling (LWD) tools operate at temperatures routinely exceeding 150°C and sometimes reaching 200°C or higher, under extreme shock and vibration from the drill string. The +200°C operating temperature of glass capacitors is one of very few dielectric technologies rated for this environment without significant derating.

High-Precision Instrumentation

In precision test and measurement equipment — metrology-grade calibrators, precision oscillators, standards-grade signal generators — the glass capacitor’s zero aging rate, freedom from piezoelectric effects, and extremely tight tolerance hold-over time make it the defensible choice for timing and frequency-determining networks where long-term calibration stability is a product requirement.

Glass Capacitor vs. Competing Technologies

The honest comparison question for any engineer specifying glass capacitors is: “When should I use glass rather than NPO ceramic, silver mica, or NP0 MLCC?” The answer depends on what you’re optimizing for.

Property	Glass	Silver Mica	NPO/C0G MLCC	Polystyrene Film
Max Temperature	+200°C	+125°C	+125°C	+85°C
Aging Rate	Zero	Near-zero	Slight (crystalline)	Near-zero
Radiation Hardness	Excellent	Good	Good	Poor
Piezoelectric Noise	None	None	Some (ceramic)	None
Hermeticity	Fully fused	Encapsulated	Not hermetic	Not hermetic
Tolerance	±0.5%	±1%	±1% (NP0)	±1%
Max Capacitance	10,000 pF	~1,000 pF	100 µF+	~10 nF
Physical Size	Larger	Large	Very small	Small-medium
Cost	Highest	High	Low	Low
MIL ER Qualification	Yes (MIL-PRF-23269)	Limited	Yes (MIL-PRF-55681)	No
Availability	Specialist	Specialist	Universal	Good

The competitive picture in short: for commercial designs at normal operating temperatures, NPO MLCC wins on size and cost. For high-temperature (>125°C) or radiation environments, glass is effectively unmatched. For space-grade applications demanding zero aging and full hermetic sealing, glass is the clear choice. Silver mica fills some of the same RF precision niche but tops out at +125°C and is approaching functional obsolescence as glass and NPO MLCC alternatives mature.

Mica is less prone to crack under mechanical shock than glass, a useful property for equipment subject to shellfire, which explains why mica was historically preferred for some shock-intensive military applications — but modern fused glass construction has closed that gap considerably.

Understanding Glass Capacitor Part Numbering

If you’re navigating a QPL for the first time, the part number structure for MIL-PRF-23269 glass capacitors follows a specific format that’s worth understanding rather than treating as an opaque string.

The DLA (Defense Logistics Agency) drawing number identifies the specific slash sheet within the MIL-PRF — for example, M23269/01 covers the CY10/CYR10 axial series (size 10), while M23269/10 covers the CYR51/52/53 radial series. The capacitance and tolerance designation follows in the dash number. A typical complete part number looks like: M23269/01-3088, which decodes to a 91 pF, ±1% tolerance CY10-size glass capacitor per MIL-PRF-23269/01.

The manufacturer’s commercial equivalents from AVX (now Kyocera-AVX) use the CY prefix with size designation directly — CY10, CY15, CY20, CY30 for the axial family, CY06, CY07, CY08 for the radial family. Both axial and radial are available.

Selecting the Right Glass Capacitor: An Engineer’s Checklist

Working through a glass capacitor selection isn’t just picking a value from a distributor catalog. In high-reliability procurement, the decision has more steps.

Step 1 — Confirm the application tier. Is this commercial hi-rel, military, or space? The answer determines whether you need MIL-PRF-23269 ER qualification, QPL listing, ESCC 3009, or NASA EEE-INST-002 compliance. Don’t over-specify (space grade costs multiples of military grade), but don’t under-specify.

Step 2 — Define operating temperature. If the maximum operating temperature is below 125°C, NPO MLCC may serve. If the requirement exceeds 125°C, glass becomes the dominant choice for small-value precision capacitors.

Step 3 — Check radiation requirements. Does the design have a total ionizing dose (TID) specification? If yes, document the glass capacitor’s radiation hardness in your design justification. This matters for space and some nuclear/downhole applications.

Step 4 — Determine required tolerance and stability. ±0.5% tolerance is available in glass. If the circuit requires better than ±1% and long-term stability, glass is one of few choices that can deliver it with full environmental immunity.

Step 5 — Verify voltage derating. For established-reliability applications, derate working voltage to 50–60% of rated voltage per MIL-HDBK-217 guidance. A 500V-rated glass capacitor should not be operated at 400V in a mission-critical design.

Step 6 — Source from QPL-listed suppliers. For military and space procurement, only parts from QPL-approved manufacturers (currently Kyocera-AVX for the CY series) are acceptable. Confirm the part appears on the current DLA QPL list before finalizing the BOM.

Leading Glass Capacitor Manufacturers and Product Lines

Manufacturer	Series	Specification	Notes
Kyocera-AVX	CY10, CY15, CY20, CY30 (Axial)	MIL-PRF-23269 QPL	Primary global supplier; formerly AVX/Corning
Kyocera-AVX	CY06, CY07, CY08 (Radial)	MIL-C-11272 / MIL-PRF-23269	Radial lead versions
Kyocera-AVX	CK Series (Glass-K)	MIL-PRF-11015 / MIL-PRF-39014	Low DA, low noise variant
Corning Glass Works	Legacy QPL parts	MIL-C-11272	Historical; AVX acquired Corning cap line

In practice, the glass capacitor market is highly consolidated. Military applications, the defense industry and the aerospace industry use glass capacitors in many of their designs. Standard Radio stocks a tremendous inventory of MIL-C-11272 and MIL-PRF-23269 glass capacitors. Kyocera-AVX (formerly AVX, which acquired the Corning Glass capacitor product line) is effectively the primary production source for new glass capacitors today. Legacy Corning Glass Works (CGW) parts are still found in military depot inventory and through specialist high-reliability component distributors for legacy equipment repair.

Useful Resources for Glass Capacitor Engineering

The glass capacitor is a niche component, and finding good technical information requires knowing where to look. These resources are the most useful:

Military Specifications and Standards

• MIL-PRF-23269F — Full text at EverySpec (everyspec.com): “Capacitors, Fixed, Glass Dielectric, Established Reliability, General Specification For.” This is the primary governing document; read it before specifying glass caps for defense work.
• MIL-PRF-11015 — Glass composition (Glass-K) established reliability specification, available through EverySpec and DLA.
• MIL-HDBK-217F — Reliability prediction for electronic equipment; includes failure rate models for glass dielectric capacitors under various stress conditions.

QPL and Product Listings

• DLA Land and Maritime Qualified Products List (QPL-23269) — Available through DLA’s ASSIST database at assist.dla.mil. This is the authoritative source for QPL-approved glass capacitor manufacturers and part numbers.
• NASA EEE-INST-002 — EEE parts selection and screening instruction for NASA programs. Available at nepp.nasa.gov.

Manufacturer Technical Documentation

• Kyocera-AVX Glass Dielectric Capacitors Datasheet — Detailed parametric tables, construction diagrams, and application guidance. Available at kyocera-avx.com.
• Federal Connectors / Standard Radio — Stocking distributors with searchable MIL part number databases for glass capacitors, including NOS (new-old-stock) Corning-era parts.

General Capacitor Engineering Reference

• For a broader technical overview spanning all capacitor technologies — including dielectric comparisons, construction types, and selection methodology — PCBSync’s capacitor resource is a useful foundation before diving into the specialized glass dielectric territory.

Standards Organizations

• ESCC (European Space Components Coordination) — ecss.nl and ESCC 3009 for space-grade ceramic and glass capacitor qualification in European space programs.
• IEC 60384-1 — General specification for fixed capacitors in electronic equipment; covers test methods applicable to glass types.

5 FAQs About Glass Capacitors

Q1: Why are glass capacitors so much more expensive than NPO ceramic capacitors of the same value?

Several factors drive the cost premium. First, the fused monolithic manufacturing process is fundamentally more complex and lower-yield than MLCC sintering. Second, established-reliability qualification under MIL-PRF-23269 requires extensive life-testing, lot screening, and documentation that doesn’t apply to commercial ceramic parts. Third, the market is far smaller — glass capacitors are made in quantities measured in thousands or tens of thousands, not the trillions-per-year volumes of MLCCs. Fourth, QPL compliance and traceability documentation add administrative overhead to every lot. The result is a component that may cost $5–$50 each versus fractions of a cent for an equivalent-value MLCC. The cost is justified when the application genuinely needs what glass provides; it’s unjustifiable overkill for a commercial PCB design.

Q2: Can I substitute an NPO/C0G MLCC for a glass capacitor in an existing design?

In many commercial hi-rel designs, a high-quality NPO MLCC from a screened lot is an acceptable substitution, provided the operating temperature stays below 125°C and there are no radiation or extreme shock requirements. However, for designs that are formally qualified to a military specification and use QPL-listed parts, a substitution requires a formal engineering change and possibly requalification — you can’t unilaterally swap a MIL-PRF-23269 glass cap for an MLCC without paperwork. The NPO MLCC will also not match the glass capacitor’s zero aging rate, full hermetic sealing, or 200°C upper temperature limit, so evaluate those properties against your specific requirements before deciding.

Q3: What does “S-level reliability” mean for glass capacitors, and do I always need it?

“S-level” (for Space) is the most stringent established-reliability designation in MIL-PRF-23269. Parts screened to S level have demonstrated a failure rate of 0.001% per 1,000 hours (1 failure per 100 million device-hours) under rated voltage at 125°C, with the tightest lot controls and most comprehensive screening. Not every high-reliability application needs S-level. R and P levels are appropriate for many military applications and carry lower cost. S-level is reserved for applications where the cost of failure is catastrophic and no field maintenance is possible — satellite electronics being the archetype. For military avionics, R-level is often sufficient. Work with your program’s reliability engineer and applicable system-level specifications to determine what reliability level is actually required.

Q4: How do I read a glass capacitor value when it’s marked with military specification codes?

Glass capacitors in military packaging are marked with the DLA drawing number, lot code, and a dash number that encodes the capacitance and tolerance. The capacitance designation uses the standard three-digit EIA code (e.g., 910 = 91 pF, first two digits significant, third is the multiplier exponent in pF), followed by a letter tolerance code (C = ±0.25 pF, D = ±0.5%, F = ±1%, G = ±2%, J = ±5%). So a part marked M23269/01-3088 decodes using the relevant slash-sheet table: the “3088” encodes 91 pF, ±1%. Datasheets and the actual MIL-PRF-23269 slash sheets are the authoritative reference for decoding these part numbers, and the EverySpec and DLA ASSIST databases are where those documents live.

Q5: Are glass capacitors still being manufactured, or is this a legacy technology?

Glass capacitors continue to be actively manufactured. Kyocera-AVX produces the CY and CK series with current QPL status under MIL-PRF-23269 and related specifications. Demand is driven by ongoing defense, space, and downhole oil-and-gas programs that specify glass dielectric for the performance properties that remain unmatched by other technologies at temperatures above 125°C. The glass capacitor is not a growing market — it’s a mature specialty — but it is stable, with committed production sources and full supply chain support. New military and space programs continue to design glass capacitors into precision RF and timing circuits where the combination of hermeticity, zero aging, radiation hardness, and high-temperature operation is required.