Contact Lens Materials: Hydrogel, Silicone Hydrogel, RGP

General product information only, not medical advice. Lens choice, fit and replacement schedule are decisions for a licensed eye care practitioner.

Short answer

Contact lens materials fall into two families. Soft lenses are made of flexible, water-absorbing plastics (hydrogels, including newer silicone hydrogels), and rigid gas permeable (RGP) lenses are firmer, more durable and resist deposit buildup. The FDA further sorts soft lenses into four groups by ionic surface charge and water content, and RGP lenses into four groups by material composition.

Definition and scope

A contact lens material is the polymer the lens is made from. It determines how the lens handles oxygen, water, deposits and care products. This guide covers the material classes that FDA documents use. It does not cover fitting, prescribing, wear schedules or cleaning technique, which belong to the eye care practitioner and the lens labeling.

The FDA describes soft lenses as being made of “soft, flexible plastics that allow oxygen to pass through to the cornea,” and notes that newer soft lens materials include silicone hydrogels “to provide more oxygen to your eye while you wear your lenses.” (FDA, Types of Contact Lenses, checked 2026-10-30.) For the general polymer concept behind soft lenses, see what a hydrogel is.

How materials are classified

Soft lenses: four groups by charge and water

FDA guidance for contact lens care products states that “there are four hydrophilic groups based on ionic surface charge and water content (Groups I, II, III, and IV).” Two properties therefore define a soft lens group: whether the surface carries an ionic charge, and how much water the material holds. The same guidance uses Group I (low water, non-ionic) and Group IV (high water, ionic) lenses as the representative lenses in care-product testing. (FDA, Contact Lens Care Products 510(k) guidance, letter dated May 1, 1997, Q&A 5, checked 2026-10-30.)

RGP lenses: four groups by composition

The same document says there are four RGP groups based on material composition. Most marketed RGP lenses fall into two of them, silicone acrylate and fluorosilicone acrylate. The pure fluoropolymer group has one polymer that is not marketed, and the last group is assorted materials that are rarely encountered.

Hydrogel versus silicone hydrogel

Both are soft lens materials. Silicone hydrogel is described by the FDA as a newer soft material intended to give the eye more oxygen during wear. It is a refinement inside the soft family, not a separate lens type.

Types at a glance

Material class	What the FDA says
Soft (hydrogel)	Soft, flexible plastics that allow oxygen to pass through to the cornea. Four groups by ionic charge and water content.
Soft (silicone hydrogel)	Newer soft material that provides more oxygen to the eye during wear.
Rigid gas permeable (RGP)	More durable and resistant to deposit buildup. Four groups by composition, mostly silicone acrylate and fluorosilicone acrylate.

Source for the table: FDA, Types of Contact Lenses, and the 1997 care-products guidance, both checked 2026-10-30. Extended (overnight) wear is usually a soft-lens category; the FDA notes that there are “a very few” RGP lenses designed and approved for overnight wear.

Types of contact lenses beyond material

Material is one way to sort lenses. The FDA also describes lens types by how long they are worn and what they are used for. (FDA, Types of Contact Lenses, checked 2026-10-31.)

• Soft and rigid gas permeable (RGP). The two material families described above.
• Extended wear. Lenses approved for overnight or continuous wear, typically soft lenses. The FDA notes that eyes need a lens-free rest for at least one night following each scheduled removal.
• Disposable and replacement-schedule lenses. The FDA defines “disposable” as used once and discarded. Most soft-lens wearers follow a frequent replacement schedule instead, and a daily disposable schedule uses a fresh pair each day.
• Orthokeratology (Ortho-K). Specialized RGP lenses that temporarily reshape the cornea; see orthokeratology.
• Decorative (plano) lenses. A specialized use that the FDA covers on its own decorative lenses page.

Where it matters for clinics and supply decisions

• Care products are matched to lens groups. Under the FDA guidance, the solution maker, not the lens maker, must demonstrate compatibility with the lens groups the solution is indicated for. A product label that names lens groups is therefore a material statement, not marketing shorthand.
• Soft and RGP are separate indications. The guidance states that changing a care product’s indication between soft lenses and RGP lenses requires a new 510(k). For how that notification works, see FDA 510(k) premarket notification.
• Material properties are tested to named standards. FDA’s March 28, 2023 performance criteria for soft (hydrophilic) daily wear lenses list water content among the tests and point to ISO 18369-4 (physicochemical properties of contact lens materials) and ANSI Z80.20. (FDA, Soft (Hydrophilic) Daily Wear Contact Lenses: Performance Criteria, checked 2026-10-30.)

Material terms to recognise on documentation

• Soft or RGP (the first split in the FDA scheme)
• Hydrophilic group I to IV (ionic surface charge and water content)
• RGP material group (for example silicone acrylate, fluorosilicone acrylate)
• Silicone hydrogel (a soft material subtype)
• Water content, reported to ISO 18369-4 and ANSI Z80.20 methods

For storage and replacement of the accessories that go with lenses, see contact lens case replacement, and for clinic-wide supply lists, the optometry clinic supply checklist. Eye rinsing products are a different category; see eye wash solution.

Contact lens base curve

Base curve is a fit parameter, separate from lens material. Under the Federal Trade Commission’s Contact Lens Rule, a contact lens prescription includes the lens power, the material or manufacturer or both, the base curve or appropriate designation, and the diameter when appropriate. (16 CFR 315.2, definition of “contact lens prescription,” checked 2026-10-31.) A seller verifying a prescription lists the same items: power, manufacturer, base curve or appropriate designation, and diameter when appropriate. (16 CFR 315.5(b), checked 2026-10-31.) The rule also bars a seller from altering a prescription; when seeking verification, that includes giving the prescriber the name of a manufacturer or brand other than the one on the prescription (16 CFR 315.5(f)). Because base curve is set by the eye care practitioner for each patient, this guide gives no values.

Common misunderstandings

• “Silicone hydrogel is a hard lens.” No. Hydrogel and silicone hydrogel are both soft materials; the silicone is there to improve oxygen supply.
• “Rigid means no oxygen.” No. RGP stands for rigid gas permeable: the material is firm but allows gas to pass.
• “Any solution works with any lens.” Compatibility is shown for specific lens groups, and soft and RGP indications differ.
• “The material tells you the fit.” It does not: base curve is a separate fit parameter (see the FAQ below).

FAQ

What are contact lenses made of?

Soft lenses are made of soft, flexible plastics that let oxygen reach the cornea, including silicone hydrogels. RGP lenses are made of firmer gas-permeable materials, mostly silicone acrylate and fluorosilicone acrylate. (FDA, checked 2026-10-30.)

What is contact lens base curve?

Base curve is a lens-fit parameter that appears on a prescription. It is set by the eye care practitioner as part of a fit, and it is not one of the FDA material groups described above. Because it is individual fit information, no values are given here.

What are the types of contact lenses?

By material: soft (hydrogel and silicone hydrogel) and rigid gas permeable. By wear and use: daily or extended wear, disposable or replacement-schedule, orthokeratology and decorative lenses. (FDA, checked 2026-10-31.)

Is silicone hydrogel the same as hydrogel?

Both are soft lens materials. Silicone hydrogel is the newer type that the FDA says provides more oxygen to the eye during wear.

Which lenses can be worn overnight?

The FDA says extended wear is usually soft lenses and that a very few RGP lenses are designed and approved for overnight wear. Wear schedules are set by the eye care practitioner.

Sources

• FTC, 16 CFR 315.2 Definitions, checked 2026-10-31.
• FTC, 16 CFR 315.5 Prescriber verification, checked 2026-10-31.
• FDA, Types of Contact Lenses, checked 2026-10-30.
• FDA, Contact lens care products 510(k) guidance (letter dated May 1, 1997), Q&A 5, checked 2026-10-30.
• FDA, Soft (Hydrophilic) Daily Wear Contact Lenses: Performance Criteria for Safety and Performance Based Pathway, issued March 28, 2023, checked 2026-10-30.