The case material is clear polycarbonate and is stronger than you might expect. In thicker sheets (2cm) this material is used as bulletproof glass. The Mooshimeter passed IEC-61010 testing, which includes a 1 meter drop test.
Regarding the sleeve: We are actually working on a sleeve, but its primary purpose is for water resistance and grip, not impact resistance. It’s still being developed though and is not yet available for sale.
Let me know if you have other questions! Best,