A flexi-tube on the snorkel mouthpiece keeps the snorkel out of the way while underwater, and can be bent back round to the most comfortable position when Required.
Better snorkels such as the TUSA Platina Hyperdry snorkel have a corrugated flexi-tube but the inside is smooth so the air flow is not disturbed making each breath much easier.
Internal corrugation causes turbulence that increases breathing resistance and makes it difficult to completely clear out the water (right). Better snorkels are smooth inside which allows the water to flow through better (left).

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