Daily disposable contact lenses are medical devices designed to be worn for a single day and then thrown away. The materials used directly affect lens comfort, oxygen flow to the eye, and overall corneal health. These thin, flexible lenses sit directly on the eye’s surface. Their composition is engineered to balance visual correction with biological compatibility, ensuring the eye can breathe and remain hydrated throughout the wearing period.
The Original Material: Water-Loving Hydrogels
The first generation of soft contact lenses was made from materials called hydrogels, which are soft, flexible, water-containing plastics. These polymers are hydrophilic, meaning they have a strong affinity for water. The most common foundational material is poly(2-hydroxyethyl methacrylate), often abbreviated as PHEMA.
Hydrogels are designed to absorb and hold a significant amount of water, sometimes ranging from 38% to over 80% of the lens mass. This absorbed water makes the lens soft and pliable, allowing it to conform to the eye. For traditional hydrogels, oxygen transport occurs almost entirely by dissolving into and traveling through this water content.
A higher water content correlates with greater oxygen permeability. However, this reliance on water creates a trade-off: a high water content lens can lose moisture and draw tears from the eye’s surface. This dehydration reduces comfort and oxygen flow, which is why a newer material was developed.
The Modern Standard: Silicone Hydrogels
Material science advanced significantly with the introduction of silicone hydrogels (SiHy). This material combines water-loving hydrogel polymers with silicone, a substance highly permeable to oxygen. The inclusion of silicone dramatically changed how oxygen reaches the eye, making breathability less dependent on water content.
Silicone is extremely effective at transporting oxygen, allowing modern lenses to achieve significantly higher oxygen levels than traditional hydrogels—sometimes up to five times greater. This superior oxygen delivery helps reduce the risk of hypoxia-related issues, which occur when the cornea does not receive enough oxygen. Since the silicone component handles most oxygen transport, SiHy lenses maintain high breathability even with a lower overall water content.
Manufacturers use various types of silicone hydrogel materials, each with unique formulations, such as senofilcon, galyfilcon, and delefilcon. These materials are now the standard for daily disposable lenses because they offer a better combination of long-term comfort and corneal health benefits for daily wearers.
Key Performance Metrics for Comfort and Health
The material composition of a daily lens translates directly into measurable metrics that affect eye health and comfort.
Oxygen Transmissibility (Dk/t)
One of the most important metrics is Oxygen Transmissibility, designated as Dk/t. The “Dk” refers to the oxygen permeability of the material itself, while the “t” (thickness) accounts for the specific design of the finished lens. A higher Dk/t value indicates a greater flow of oxygen to the cornea, which is necessary to prevent swelling and maintain tissue health.
Water Content
Water content affects initial comfort and wettability. In silicone hydrogels, water content often ranges between 30% and 50%. While water provides a cushion and lubricity on insertion, the silicone component ensures that the lens remains highly breathable even if some water evaporates over hours of wear.
Modulus
The Modulus describes the material’s stiffness or resistance to deformation. A lower modulus indicates a softer, more flexible lens, which contributes to better wearer comfort. Because silicone is a relatively stiff material, manufacturers work to minimize the modulus of silicone hydrogels. This ensures the lens remains soft and easy to handle while still providing superior oxygen flow.