Oxygen permeables are made of a firm, durable plastic that transmits oxygen. The rigidity of oxygen permeables also means they are easier to handle than soft lenses. And since they retain their shape better, they provide crisper vision. Don't confuse oxygen permeable contacts with hard lenses. Oxygen permeables may be firm, but they are not the uncomfortable hard lenses of the past, which didn't allow much oxygen to reach the eye.
Hard lenses are obsolete nowadays.
Oxygen permeable lenses are custom made for each individual. Your eyecare practitioner will measure the exact shape of your cornea and prescribe lenses with the curvature, size, and corrective power that suit your particular eyes. They offer better initial comfort and most will last for up to a year with proper care. Soft contacts range from disposable lenses, replaced every day, every few weeks or every few months, to daily wear lenses that are removed nightly. Most soft contact lenses are mass produced in limited sizes and in a wide range of corrective powers.