Silicone, translucent or FKM (Viton), black.

Silicone tubing
Very good temperature resistance
Autoclavable (121 °C)
Limited chemical resistance when used with concentrated acids

FKM (Viton) tubing
FKM tubing is known for its resistance to oils and chemicals, this remarkable material retains its good mechanical and chemical resistance properties at extremely high temperatures better than any other known elastomer. FKM is also a standout material in its resistance to weather-related aging and ozone.