Short answer: The three families differ in two separate properties that often get collapsed into one. COE is how much the glass expands when heated, which is what governs compatibility and annealing; how hot you must get it to work is a matter of viscosity and composition. The two track each other across these families, but COE is not the cause. Soft glass (soda-lime) sits around COE 104, softens at the lowest temperature, and is the home of beads and soft-glass art, it’s the easiest to melt and the friendliest to a modest torch and oxygen supply. Borosilicate (“boro”) is around COE 33, runs hotter and stiffer, and is the glass of pipes, sculpture, and marbles, it wants more torch and more oxygen. Quartz (fused silica) has a near-zero COE and an extremely high softening point (~1683 °C), which is why it lives in the scientific/technical world, where hydrogen with oxygen is the standard fuel for sustained work. Match your glass to your torch’s heat, your oxygen, and your eyewear, not the other way around.
If you’re choosing a torch around the glass you want to work, start with the complete glass torch buyer’s guide, then come back here to understand what each glass actually demands.
What COE is (and why it decides everything else)
COE stands for coefficient of expansion, how much a glass expands and contracts as its temperature changes. A soda-lime glass with a COE of 104 expands about 0.0000104 inches per inch for each °C of temperature change; borosilicate at ~33 expands and contracts far less over the same swing. Source: Bullseye Glass, TechNote 3.
Two things fall out of COE that matter at the bench:
- Compatibility. Glasses of different COE are incompatible, mix a 104 bead with a 33 boro cane and the join will crack as it cools. You generally work within one family at a time. Source: Bullseye Glass, TechNote 3.
- Working temperature. Lower-COE glasses tend to be stiffer and need more heat to move. That’s the through-line of this whole article: soft glass is the coolest and easiest to work, boro is hotter, and quartz is hottest by a wide margin.
Soft glass (soda-lime), ~104 COE, the beginner-friendly default
What it is: Soda-lime “soft glass,” the classic beadmaking and soft-glass-art material (Effetre/ Moretti, Vetrofond, and similar lines are all in this family). Typical lampworking COE is around 104 (the broader soft-glass world spans roughly 90 to 104). Source: Science Insights.
Working-temp character: The lowest of the three. Soda-lime softens in the ~700 °C range and becomes fluid and workable well below the temperatures boro needs, the soda and lime act as a flux that lowers the melting point of the silica. Source: Science Insights. That low working temperature is exactly why beginners start here: it melts without a fight.
Torch power and oxygen: The most modest of the three. Soft glass runs happily on entry and mid-size bench torches and a single oxygen concentrator, you don’t need a monster burner or bulk oxygen to make beads. If you’re sizing your oxygen to your torch, see how many LPM does my torch need; a forgiving, gentle surface-mix flame is a common soft-glass recommendation.
Eyewear note: Heating soda-lime throws a bright orange-yellow sodium flare at ~585 nm. Didymium lenses are made to filter exactly that flare, which is why they’re the standard soft-glass eyewear; Phillips Safety rates its own didymium-family lenses for UV as well, but check the exact lens’s specification rather than the family name (see didymium vs ACE glasses). Source: Phillips Safety.
Borosilicate (“boro”), ~33 COE, hotter and tougher
What it is: Borosilicate glass, the same family as Pyrex/Duran, and the dominant material for pipes, sculpture, and marbles. Lampworking boro is “33 COE” glass; the underlying borosilicate 3.3 standard has a coefficient of about 3.3 × 10⁻⁶ /K (i.e., ~33 in the lampworker’s shorthand). Source: Wikipedia, Borosilicate glass. The Pyrex, Duran and Simax history covers how those brands relate.
Working-temp character: Hotter and stiffer than soft glass. Borosilicate’s softening point is around 820 °C (Pyrex 7740), noticeably above soda-lime’s, so boro stays rigid through temperatures where soft glass is already flowing, and it needs more sustained heat to move. Source: Wikipedia, Borosilicate glass.
Torch power and oxygen: More than soft glass. Boro work, especially larger sculpture and thick tube, rewards bigger, hotter torches and more oxygen (often multiple concentrators or bulk/compressed oxygen for serious pieces). Small boro is within reach of mid-size beginner torches, but as the work scales up so does the appetite; size your supply with how many LPM does my torch need.
Eyewear note: Boro demands more than didymium alone. In addition to sodium flare, hot boro emits infrared (IR), and didymium does not block IR. Serious boro work pairs sodium-flare filtration with a welding shade (commonly Shade 3 or greater) or a lens the maker rates for boro, such as Phillips’s BoroTruView, for UV and IR protection; the boro shade guide covers choosing one. Source: Phillips Safety, VetroSafe.
Quartz (fused silica), near-zero COE, the high-temperature specialist
What it is: Fused quartz / fused silica, essentially pure silica. It’s the scientific and technical glass (lab ware, semiconductor tubes, high-temperature apparatus), and a specialty in art glass rather than an everyday beginner material.
COE and working-temp character: Quartz has an extraordinarily low coefficient of thermal expansion, about 0.55 × 10⁻⁶ /°C, far below even boro, which is what gives it such extreme thermal-shock resistance. The flip side is a very high softening point of roughly 1683 °C, so it takes far more heat to work than soft glass or boro. Source: Machined Quartz.
Torch power and oxygen: The most demanding of the three. Scientific-glassblowing practice treats hydrogen with oxygen as the standard fuel for quartz, partly for the clean burn (more on that below), though it is not the only route: Nortel documents its Nortel Unitorch family, which our catalog records on propane and natural gas, for 40 mm quartz tubing. Source: Scientific Glassblowing Learning Center, “Gases”.
Eyewear note: Quartz work runs at higher temperatures and produces intense radiant output, so appropriate high-temperature filtration (sodium-flare plus IR-rated welding shades) is essential, treat it as at least as demanding as boro, and follow the guidance for your specific process and flame.
Can you use hydrogen?
Yes, for the right glass. Hydrogen burned with oxygen (an “oxyhydrogen” or hydrogen-oxygen flame) burns exceptionally cleanly, and it’s the classic choice for quartz.
Why it’s cleaner. Hydrogen’s only combustion product is water vapor, so the flame is essentially contaminant-free, there’s no carbon to deposit on the work, which matters for optically clean, high-purity quartz.
When it’s used. Quartz is the headline case, and Herbert Arnold’s catalog shows it in hardware: its Zenit burner is rated for borosilicate on propane and natural gas and adds quartz only on the hydrogen version. The full evidence, and the safety handling hydrogen needs, is in hydrogen vs propane for glassworking. Source: Scientific Glassblowing Learning Center, “Gases”.
Where it doesn’t belong. Hydrogen is not typical for soft glass. Soda-lime softens around 700 °C and works easily on ordinary oxy-propane (or natural gas), adding a harder-to-manage fuel buys you nothing but risk for beadwork.
Cautions. Hydrogen is its own animal: it’s lighter than air (it rises and disperses, the opposite of propane), has a very wide flammability range and a low ignition energy, and burns with a flame that can be nearly invisible in daylight. Supply and handling differ too: it comes from specialty gas supply rather than the bottled propane most benches already have. If you move to hydrogen, treat it as a deliberate equipment and safety decision: correct regulators and fittings for hydrogen, the flashback protection your torch and gas supply call for, good ventilation, and the manufacturer’s guidance for your torch and fuel. For the broader fuel picture (and why propane stays the default for most studios), see propane vs natural gas for torchwork.
Side-by-side: soft glass vs boro vs quartz
Numbers below are typical/approximate and rounded, confirm specifics for the exact glass and torch you’re using before relying on them.
| Factor | Soft glass (soda-lime) | Borosilicate (“boro”) | Quartz (fused silica) |
|---|---|---|---|
| COE | ~104 | ~33 (3.3 × 10⁻⁶ /K) | ~0.55 × 10⁻⁶ /°C (near-zero) |
| Working-temp character | Lowest; softens ~700 °C | Hotter/stiffer; softens ~820 °C | Highest; softens ~1683 °C |
| Typical work | Beads, soft-glass art | Pipes, sculpture, marbles | Scientific / technical |
| Torch & oxygen | Modest, entry/mid torch, single concentrator | More, bigger/hotter torch, more oxygen | Most, often hydrogen-oxygen |
| Eyewear | Didymium (sodium flare) | Didymium + welding shade (IR) | High-temp IR-rated filtration |
| Hydrogen? | Not typical | Not typical | The standard fuel in scientific practice |
Sources: Bullseye Glass, TechNote 3, Wikipedia, Borosilicate glass, Machined Quartz, Oxyhydrogen, Scientific Glassblowing Learning Center, Phillips Safety.
How this maps to your torch decision
The practical takeaway is that glass choice and torch choice are the same decision, made twice:
- Working soft glass? A modest, forgiving setup is plenty. A gentle surface-mix flame on a single oxygen concentrator handles beads beautifully.
- Moving into boro? Plan for more heat and more oxygen, and upgrade your eyewear for IR. Size the oxygen with how many LPM does my torch need.
- Chasing quartz? That’s a specialist path, usually on a hydrogen-oxygen flame with the extra handling that comes with it; read hydrogen vs propane for glassworking for the fuel side, and propane vs natural gas for torchwork for the everyday fuels, before you commit.
For the full setup, torch, oxygen, fuel, and safety together, work through the complete glass torch buyer’s guide.
Key takeaways
- Soft glass (soda-lime), ~104 COE: lowest working temperature (softens ~700 °C), beads and soft-glass art, modest torch and a single concentrator, didymium for sodium flare.
- Boro (borosilicate), ~33 COE: hotter and stiffer (softens ~820 °C), pipes/sculpture/marbles, bigger torch and more oxygen, didymium plus a welding shade because boro also emits IR.
- Quartz (fused silica), near-zero COE: highest working temperature (softens ~1683 °C), scientific/technical work, usually on a hydrogen-oxygen flame, high-temp IR-rated filtration.
- COE governs compatibility, don’t mix families; different COEs crack on cooling.
- Hydrogen-oxygen is the classic quartz flame and burns cleaner (product is water). It’s used for quartz, not for soft glass, and it brings its own handling and safety considerations.
- All figures here are approximate, confirm the specs for your exact glass, torch, and flame.
Sources
- Bullseye Glass, “TechNote 3: Compatibility of Glass”: https://www.bullseyeglass.com/technotes-3-compatibility-of-glass/
- Science Insights, “What Is Soft Glass? Soda-Lime Glass Explained”: https://scienceinsights.org/what-is-soft-glass-soda-lime-glass-explained/
- Wikipedia, “Borosilicate glass”: https://en.wikipedia.org/wiki/Borosilicate_glass
- Machined Quartz, “Thermal Properties of Fused Quartz”: https://machinedquartz.com/thermal-properties-of-fused-quartz/
- Wikipedia, “Oxyhydrogen”: https://en.wikipedia.org/wiki/Oxyhydrogen
- Scientific Glassblowing Learning Center, “Gases”: https://www.ilpi.com/glassblowing/tutorial_gases.html
- Phillips Safety, “Didymium Glasses”: https://phillips-safety.com/didymium-glasses/
- VetroSafe, “Guide to Safety Ratings for Lampworking Glasses”: https://vetrosafe.com/blogs/news/guide-to-ratings-for-lampworking-safety-glasses
Editor’s note: COE, softening-point, and flame-temperature figures are typical/approximate values drawn from public sources as of 2026 and rounded for comparison; they vary by specific glass formulation and measurement method. Verify the numbers for your exact glass and follow the manufacturer’s instructions and qualified professional advice for your torch, fuel, and eyewear.