Most have ceramic or ceramic-coated plates (some with the addition of titanium, alumina, nano silver, silk proteins, tourmaline, etc.) which are claimed to eliminate frizz and static charge in hair to leave it smooth and shiny.
Ionic straighteners. Basic science says opposites attract - so by using a negatively charged straightener on hair that tends to be positively charged, you’d expect to get neutral hair, i.e. no charge, which helps control frizz. The flow of negative ions (plus heat) from the straightener also attach to and reduce the size of water vapour particles on the hair, which also aids in flattening of the hair shaft to produce a smooth, shiny looking surface
Tourmaline is a semi-precious gem. The idea is that the ceramic plates or coatings are “infused” with powdered tourmaline (or other such minerals) to generate even more negatively charged ions, enhancing the anti-frizz and smoothing effects of the hair straightener.
Far infrared heat. Manufacturers claim this is better for your hair as high heat only applied to the exterior of the hair shaft can be more damaging and drying. Heating from the inside out results in smoother, shinier hair due to less damage to the exterior of the hair cuticle.