reversed faces

i made a model in 3ds max and i used a symmetry modifier to make it easier but when i put the symmetry modifier on it it was on backwards so i flipped the direction and now when i put the model into unity all the faces are reversed, as in if i look at a model the side closer to me is see through and the side further away is visible and i can see the texture on it. does anyone know how to fix this?

In 3ds max, open object properties and enable backface cull, this hides the backs of polygons.
Throw a normals modifier on the model to flip the polygons, or just flip them individually.