"Why do you need a sheath?
There's a cover over the business end to protect it."
Lemme tell you a story:
Last November, when we reached our first campsite in the Grand Canyon, my wife collected the water bottles, dug the Steripen (Journey) out of her pack and stuck it in her pockets, and walked to the water source. When she bent down the Steripen popped out of her pocket - orange cover still in place - and fell onto rock. It still looked fine, even showed the smiley face, but the lamp wouldn't light. Fortunately I'm paranoid enough that we had enough ClO2 tabs for drinking water to get us to Indian Garden, and enough extra alcohol to bring all our "cooking" water to a full boil instead of my normal barely simmering.
The repair wasn't cheap; I still use it but I don't take it for granted.