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randomray never use any tubes when doing a head cast. If you put a straw or tube in the mold you run the danger of the alginate dragging the tube out of the orifice you have it in. Long story short your model will not be able to breathe. Easy fix when molding get the subject to blow the alginate out of their nose after you put it around the nose. This creates a air hole that they can breathe out of. Much easier and you dont run the risk of hurting your model or yourself.