Colored polycarbonate: colored tunnels (e.g., red or yellow) allow for low-light shelter for your mice, while still allowing for health observation.
Cardboard/recycled paper: cardboard tunnels are disposable (and therefore do not require additional cleaning/sanitation). They also provide mice with a source of sheltering, nesting, and gnawing enrichment, and can help reduce boredom or aggression. However, they can obstruct health observations by animal care staff and must be replaced much more frequently than reusable tunnels.
Lifespan/replacement: Most tunnels (plastic/polycarbonate) last about 3 years.
Tunnel size: you want to be sure your tunnels are large enough to fit your mice, but small enough to fit in the cage and not get stuck. Tunnels for mice are typically 5 cm wide and 10 to 15 cm long.