Borosilicate glass is the material of choice for laboratory glassware across pharmaceutical, research, analytical, and academic laboratory environments worldwide. If you have ever worked in a laboratory, you have almost certainly used borosilicate glass without giving much thought to what makes it different from ordinary glass — or why it is the universally accepted standard for laboratory use rather than any of the alternatives. This guide covers everything you need to know about borosilicate glass in the laboratory: what it is, how it is made, what its key properties mean in practice, where it is used, what it cannot do, and how to select the right borosilicate glassware for your specific laboratory application in Ireland.
Borosilicate glass is a type of glass manufactured using silica (silicon dioxide, SiO₂) and boron trioxide (B₂O₃) as the primary glass-forming components, alongside smaller quantities of aluminium oxide (Al₂O₃), sodium oxide (Na₂O), and other minor oxides. The incorporation of boron trioxide into the silica glass network is what fundamentally distinguishes borosilicate glass from ordinary soda-lime glass — and what gives borosilicate its unique combination of thermal, chemical, and mechanical properties that make it so well-suited to laboratory use.
The typical composition of borosilicate 3.3 glass — the grade universally used for laboratory glassware — is approximately 81% silicon dioxide, 13% boron trioxide, 4% sodium oxide, and 2% aluminium oxide by weight. The designation "3.3" refers to its coefficient of thermal expansion: 3.3 × 10⁻⁶ K⁻¹. This number is the single most important characteristic of the material and underpins most of its practical advantages in laboratory use.
Borosilicate glass was first developed in the late 19th century by German chemist Otto Schott, working with Carl Zeiss in Jena, Germany. The brand name Pyrex — introduced by Corning in the early 20th century — brought borosilicate glass to widespread attention, though today the term Pyrex refers to a range of products rather than a specific glass composition. In the laboratory context, the relevant specification is always borosilicate 3.3 to ISO 3585 — the international standard that defines the material properties required for laboratory glassware.
To understand why borosilicate glass performs so differently from ordinary glass, it helps to understand what happens at the molecular level when boron trioxide is incorporated into a silica glass network.
In ordinary soda-lime glass (the glass used in windows, bottles, and everyday glassware), the silica network is modified by sodium and calcium oxides. These modifier oxides break Si-O-Si bonds in the network, introducing non-bridging oxygen atoms that make the glass easier to melt and process — but also weaker, more chemically reactive, and more susceptible to thermal shock.
When boron trioxide is added instead, boron atoms participate in the glass network as either three-coordinated (BO₃ triangles) or four-coordinated (BO₄ tetrahedra) units. In the borosilicate 3.3 composition, the boron atoms largely take a tetrahedral coordination — effectively joining the silica network as a second network-forming oxide rather than acting as a modifier. The result is a much more cross-linked, rigid, and thermally stable glass network with significantly fewer non-bridging oxygen atoms than soda-lime glass.
This structural difference at the molecular level is directly responsible for every practical property advantage that borosilicate glass has over ordinary glass in laboratory use.
The coefficient of thermal expansion (CTE) measures how much a material expands or contracts per degree of temperature change. For borosilicate 3.3 glass, this value is 3.3 × 10⁻⁶ K⁻¹ — approximately one third of the CTE of ordinary soda-lime glass (approximately 9 × 10⁻⁶ K⁻¹). This means that for the same temperature change, borosilicate glass expands or contracts about three times less than soda-lime glass.
The practical consequence is exceptional thermal shock resistance. When a cold glass vessel is filled with a hot liquid, or a hot vessel is placed on a cold surface, the differential expansion between the hot and cold regions of the glass creates internal stress. In soda-lime glass, this stress frequently exceeds the mechanical strength of the glass and causes cracking or shattering. In borosilicate 3.3 glass, the smaller expansion means the stress remains well within the glass's mechanical tolerance — allowing it to withstand temperature differentials of up to 160°C without failure under normal laboratory conditions.
This property makes borosilicate glass safe to use on hotplates, in ovens, during direct heating with a Bunsen burner, during autoclaving, and in applications where hot solutions are added to room-temperature vessels — all routine laboratory operations that would be hazardous with ordinary glass.
Borosilicate 3.3 glass provides excellent resistance to chemical attack across a wide range of reagents. Its chemical durability is classified under three international standards:
The excellent acid and hydrolytic resistance of borosilicate 3.3 glass means it does not leach significant quantities of ions into solutions stored or prepared within it — an important consideration for pharmaceutical QC, where contamination of reference standards, assay solutions, or samples could compromise analytical results. This property also qualifies borosilicate glass as a Type I glass under the United States Pharmacopeia (USP) classification system — the highest category for pharmaceutical glass containers.
Borosilicate 3.3 glass transmits light well across the UV-Vis spectrum from approximately 300nm upwards — making it appropriate for UV-Vis spectrophotometry applications using glass cuvettes and for visual observation of reactions and samples. Below approximately 300nm, UV transmission decreases, and quartz or fused silica cuvettes are required for deep UV measurements.
The optical clarity of borosilicate glass also makes it practical for visual monitoring of liquid levels, colour changes, and precipitate formation in laboratory vessels — a straightforward advantage over opaque plastic alternatives.
Borosilicate 3.3 glass has a density of approximately 2.23 g/cm³ and a Vickers hardness of approximately 550 HV — comparable to other borosilicate formulations. While borosilicate glass is stronger than soda-lime glass in terms of thermal shock resistance, it remains a brittle material and will fracture under sufficient mechanical impact. Proper handling practices — including not placing glass vessels on hard surfaces without cushioning, avoiding thermal shock beyond the material's tolerance, and inspecting glassware for chips or cracks before use — remain important regardless of glass composition.
Borosilicate 3.3 glass can be used continuously at temperatures up to approximately 500°C and intermittently at higher temperatures. The softening point is approximately 820°C and the annealing point approximately 560°C. These high-temperature properties make borosilicate glass suitable for use in laboratory furnaces, high-temperature reactions, and repeated autoclaving cycles at standard sterilisation temperatures of 121°C — applications for which ordinary glass or most plastics are not suitable.
Soda-lime glass is the most common glass type globally — used for windows, beverage bottles, food jars, and most everyday glass items. It is significantly cheaper to produce than borosilicate glass. However, in laboratory contexts, its limitations make it unsuitable for most analytical and pharmaceutical applications:
| Property | Borosilicate 3.3 | Soda-Lime Glass |
|---|---|---|
| Thermal expansion (CTE) | 3.3 × 10⁻⁶ K⁻¹ | ~9 × 10⁻⁶ K⁻¹ |
| Thermal shock resistance | Excellent — up to 160°C differential | Poor — prone to cracking |
| Chemical resistance | Excellent (Class S1 acid, Class HGB1 hydrolytic) | Moderate — higher ion leaching |
| USP glass classification | Type I — highest grade | Type III — general purpose only |
| Suitable for autoclave | Yes — repeated cycles | Limited |
| Suitable for heating | Yes — direct flame, hotplate, oven | No — high breakage risk |
| Ion leaching into solutions | Minimal | Significant at elevated temperature |
| Relative cost | Higher | Lower |
| Laboratory suitability | All laboratory applications | General purpose only — not pharma QC |
For pharmaceutical QC, regulated research, and any analytical application where sample or solution integrity is important, borosilicate 3.3 glass is the only appropriate choice. Soda-lime glass labware should not be used in validated analytical methods or GMP-regulated testing environments.
At the other end of the spectrum from soda-lime glass, quartz glass (fused silica) offers even higher thermal and chemical resistance than borosilicate. Quartz glass has a CTE of approximately 0.55 × 10⁻⁶ K⁻¹ — about six times lower than borosilicate 3.3 — and can withstand continuous temperatures above 1000°C. It also provides excellent UV transmission down to approximately 150nm, making it the required material for deep UV spectroscopy cuvettes.
However, quartz glass is significantly more expensive to manufacture than borosilicate, and for the vast majority of routine laboratory applications — including all standard volumetric glassware, reaction vessels, funnels, and general-purpose labware — borosilicate 3.3 provides all the thermal, chemical, and optical properties required, at a fraction of the cost of quartz. Quartz glassware is reserved for specialist high-temperature or deep UV applications where borosilicate's properties are genuinely insufficient.
Borosilicate 3.3 glass is used across virtually every category of laboratory glassware. In Irish pharmaceutical, research, and analytical laboratories, the most common applications include:
All certified volumetric glassware — including volumetric flasks, measuring cylinders, volumetric pipettes, and graduated pipettes — is manufactured from borosilicate 3.3 glass. The low CTE and minimal ion leaching of borosilicate glass are particularly important for volumetric instruments, where thermal stability ensures consistent internal dimensions at the calibration temperature and chemical inertness prevents contamination of standard solutions.
Borosilicate 3.3 DIN graduated beakers are the standard vessel for mixing, heating, dissolving, and containing liquid samples across all laboratory disciplines. Their thermal shock resistance makes them safe to heat on hotplates and Bunsen burners, and their chemical resistance makes them suitable for the full range of reagents encountered in pharmaceutical and analytical chemistry.
Round bottom flasks, flat bottom flasks, Erlenmeyer conical flasks, and filtration flasks are all manufactured from borosilicate 3.3 glass. The thermal and chemical resistance of the material is particularly important for round bottom flasks used in heating mantle applications, rotary evaporation, and vacuum distillation — applications where both high temperature and mechanical stress under vacuum are present simultaneously.
Borosilicate 3.3 glass laboratory funnels and separating funnels are used for filtration, liquid transfer, and liquid-liquid extraction. The chemical resistance of borosilicate glass to the organic solvents used in liquid-liquid extraction is a critical practical requirement — solvents such as dichloromethane, ethyl acetate, and chloroform would attack less chemically resistant materials.
Beyond laboratory glassware, borosilicate glass is used for pharmaceutical primary packaging — ampoules, vials, syringes, and cartridges for injectable medicines. USP Type I borosilicate glass is required for the most chemically sensitive injectable formulations. The hydrolytic resistance of the glass ensures that the packaging does not interact with the drug product or alter its pH — a requirement directly relevant to drug safety and stability.
Despite its excellent overall properties, borosilicate 3.3 glass has several limitations that laboratory professionals should be aware of:
When purchasing laboratory glassware, confirming the glass specification is important — particularly for pharmaceutical QC and regulated research applications where the material specification of laboratory equipment may need to be documented as part of supplier qualification records.
Borosilicate 3.3 laboratory glassware is typically identified by:
All Glassco laboratory glassware available from Varen Scientific is manufactured from borosilicate 3.3 glass to ISO 3585 and complies with the relevant ISO and DIN product standards for each glassware type.
Varen Scientific supplies a comprehensive range of Glassco borosilicate 3.3 laboratory glassware to pharmaceutical, research, and analytical laboratories across Ireland — including beakers, measuring cylinders, volumetric flasks, laboratory flasks, laboratory funnels, and graduated pipettes. All products are supplied from Glassco's European warehouse in the Netherlands for fast and reliable delivery across Ireland, with conformity certificates available for certified Class A and Class AS volumetric items to support your supplier qualification documentation.
For further technical information on borosilicate glass properties and international glass standards, refer to guidance published by ISO (International Organisation for Standardisation). To discuss your laboratory glassware requirements or request a quote, contact our team directly or use the Request a Quote button on any product page.
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