One customer’s records

My Kazumi flask cracked during the fourth use

What happened, how I used it, and what I can confirm.

Published August 2, 2026Last fact-checked August 2, 2026Written by the purchaser

What happened

The lower flask cracked during my fourth use on July 18, 2026. Kazumi’s support system acknowledged my ticket that day. The retained records contain the automated acknowledgment but no substantive response.

I have not had the flask examined by an expert, so I do not claim to know the engineering cause.

Use conditions

Date of use: July 18, 2026
Heat source: Gas stove, medium-high heat
Starting water amount: 400 ml
Starting water temperature: Room temperature
Heated empty: No
Prior impact or chip: None

Lower glass flask with several visible cracks extending across its base — Public derivative of the supplied photograph. Device and capture metadata were removed; no content was added, removed, or retouched.

Instructions

My package did not contain printed brewing instructions or printed heat-safety warnings. Kazumi does publish instructions online.

What Kazumi’s current online guidance says

The current Brew Guide begins with room-temperature water. The FAQ warns that sudden temperature changes or impact can break borosilicate glass. A longer guide also warns against heating without water, adding cold water to hot glass, and uneven gas-stove heat.

I cannot establish whether those pages used the same wording when I purchased the brewer.

Prior assembly issue

Before the crack, I contacted Kazumi because the connecting tube touched the bottom of the flask. Kazumi said the issue was common during initial assembly and instructed me to rotate the glass while applying gentle pressure. This site does not imply that the assembly issue caused the later crack.

Conclusion

A flask cracking during its fourth use was unacceptable to me. The crack and use conditions are documented here; the engineering cause remains unresolved.