Unworked Glass Tubes — Low Thermal Expansion (≤5×10⁻⁶/K)

The thermal expansion coefficient is typically established by the manufacturer's technical data sheet or a third-party materials test report. CBP may request this documentation to confirm classification under 7002320000 versus the residual glass tube heading. Importers should retain test certificates in their entry records, as post-entry audits in the glass sector sometimes focus on this specification boundary.

Both countries host long-established borosilicate glass producers with vertically integrated operations — from raw batch formulation through precision tube drawing — that supply pharmaceutical, laboratory, and industrial customers globally. Their technical consistency and regulatory compliance documentation (important for pharmaceutical-grade tubing) make them preferred sources for US buyers requiring tight dimensional and chemical tolerances.