**Yes—very hot water can contribute to cracking, especially in a wooden mate.** Sudden changes in temperature and moisture are a concern: [Almacén Argentino’s palo santo care guide](https://almacenargentino.com/es/index.php?controller=attachment&id_attachment=2) specifically warns about these and advises warm water for curing, avoiding boiling water.

Your three failures need slightly different explanations:

- **The one that leaked during the cold-water soak:** hot water cannot explain that failure if none had been added. A pre-existing crack or weakness is a plausible explanation.
- **The wooden one:** excessively hot water could have contributed. The wood’s condition and preparation also matter; curing cannot reliably rescue an inherently weak vessel. [Yerba Mate Lab](https://yerbamatelab.com/blogs/blog/how-to-cure-a-wooden-gourd) discusses both water temperature and poor-quality wood as causes of cracking.
- **The natural calabash:** leaving damp yerba inside for about a day is a common curing method. That step alone does not establish that you made a mistake. [RioMates’ curing guidance](https://riomates.com.ar/blog/como-curar-mate-calabaza) uses hot, non-boiling water during the process.

For a replacement, follow instructions for its particular material. Wooden mates—especially palo santo—may have an oiling step before the damp-yerba treatment. Use warm water for curing, avoid pouring boiling water into the vessel, and let it dry naturally after use. For drinking, **around 70–75°C (158–167°F)** is a cautious starting point; this is practical guidance, not a guaranteed crack-prevention threshold.

Given that one leaked before its first hot-water use, **there is good reason to suspect a defect in at least that one**. For the other two, the actual water temperature and their condition before use would be needed to distinguish preparation damage from material defects.