Although Unbreakable and iFlex are very similar and are used for the same indications, there are some differences to be mentioned.
Unbreakable is a nylon-based material, this technology has been used for flexible partials for over 60 years, and has long-lasting proven success. It is a durable material that is guaranteed unbreakable under normal usage. Adjusting Unbreakable is simple, however, it takes some specialty skills. Pink Zirconia Burs, green points and brown rubber points are recommended when adjusting.
iFlex is a newer technology that was launched in 2012, it is a polyolefin-based material. It is durable and clinically unbreakable under normal usage. iFlex tends to be easier to adjust and is slightly more translucent than Unbreakable. It is also slightly more flexible, although flexibility of both products will depend on design and thickness of the partial. iFlex can be adjusted with Pink Zirconia Burs and most carbide burs.
Both materials, are formulated for removable flexible partials with aesthetic, functionality, and patient comfort in mind. Deciding which material is simply a matter of preference by you and the dental technician.