For high-altitude use, portability and weight are the most critical factors. You should prioritize Aluminum Alloy (6061) or Carbon Fiber Composite cylinders over traditional steel, as they are significantly lighter and easier to carry during trekking or climbing. For individual emergency use, a capacity of 0.5L to 2L is standard, while 5L to 10L units are better suited for base camp medical stations. Ensure the cylinder has a working pressure of at least 150-200 bar to provide sufficient oxygen volume in a compact size.