What is the difference between BK7 and K9 optical glass?

Update Time:2026/4/28

BK7 and K9 are the two most widely used optical glass materials in the global optical industry, often seen as interchangeable alternatives. Many customers ask about their differences, so let’s break down the key similarities and distinctions clearly.

BK7, also known as borosilicate crown glass, is a European standard optical glass defined by ISO and DIN specifications. It is manufactured under strict international quality control systems, ensuring consistent optical performance across all production batches. K9, on the other hand, is the Chinese equivalent of BK7, formulated to match BK7’s optical and physical properties to the highest possible degree. Both materials share nearly identical core parameters, including a visible light transmittance of over 91%, a low thermal expansion coefficient, excellent chemical resistance, and outstanding machinability.

The primary difference between BK7 and K9 lies in their regional manufacturing standards and certifications. BK7 is widely recognized and accepted in European, American and other Western markets, while K9 is the preferred choice in Asian markets. In most practical applications, such as optical lenses, prisms, optical windows and industrial optical components, the two materials are fully interchangeable, as their refractive index, dispersion, and other key optical specifications are nearly identical. For example, if you are producing a standard camera lens, microscope component or industrial optical window, K9 can serve as a cost-effective alternative to BK7 without sacrificing any performance.

Another minor difference is the production process and quality control standards. While both materials meet high-quality requirements, some manufacturers may have slight variations in their production processes, leading to minor differences in surface quality or batch consistency. However, these variations are usually negligible for most industrial and commercial applications, especially when working with a reliable supplier like Felix Glass.

Our factory provides both BK7 and K9 optical glass parts with customized processing services, including precision cutting, surface polishing, anti-reflective coating and CNC machining, to meet the specific requirements of your projects. Whether you need BK7 optical glass for international projects or K9 optical glass for cost-effective solutions, we can deliver high-quality products that meet your exact specifications.

Previous What are the key advantages of BK7/K9 optical glass?

Next How can I get a fast quotation for my optical glass project?

Learn more from our FAQ

What is your MOQ for custom optical glass and display glass parts?: Felix Glass offers highly flexible MOQ to support client projects, including prototype testing, small batch trial orders and large-volume mass production. All products can be fully customized according to your drawings, tolerances and application standards. Send us your specs to get an accurate price quote within 24 hours.

Can I get free glass samples for testing before bulk order?: Yes, our FELIX GLASS factory supports sample testing for a wide range of precision optical glass components and assemblies. The lead time for sample production is 3 to 7 working days. Please contact us today to arrange samples and obtain a customized solution that meets your needs.

What is the production lead time for custom optical glass components?: What is the production lead time for custom optical glass components?
Answer: The lead time for standard samples is 3–7 business days, while mass production takes 15–25 business days, depending on product complexity and order volume. We provide reliable, rapid delivery for orders serving the industrial, medical, automotive, and aerospace sectors. Please submit your project details to receive an accurate delivery schedule.

Are your optical glass products ISO, CE and RoHS certified?: All FELIX GLASS precision optical glass components comply with ISO quality system standards, as well as CE and RoHS requirements. We provide comprehensive test reports, material certificates, and inspection documentation for customer review. Please feel free to request full certification details and a formal quotation today.

Do you offer one-stop custom optical glass processing services?: Yes. We provide a full range of in-house processing services, including CNC machining, precision grinding, optical polishing, vacuum coating (AR, AF, AG, IR), tempering, and screen printing. Every step—from raw material to finished product—is carried out within our own facility. Please let us know your requirements, and we will provide you with the most cost-effective solution.

CONTACT US NOW FOR A QUOTE

Send an inquiry now—we will respond promptly within 1–24 hours and provide our best formal quote within 1–2 days! Let’s start a mutually beneficial partnership today...

*Email

Name

*Title

*Content

Agree to use terms of service,Terms & Conditions

Send

What is the difference between BK7 and K9 optical glass?

A specialist in precision optical glass with 19 years of experience, providing comprehensive, satisfying custom solutions.

A specialist in precision optical glass with 19 years of experience, providing comprehensive, satisfying custom solutions.