Rubber and TPR handles from the catalog
Rubber handles put a rubber or rubberlike surface where the hand grips the knife: sometimes the whole handle, sometimes an insert, and sometimes an overmold, a rubber layer molded over a rigid frame. Böker's glossary entry on rubber calls it "a versatile material used in knife production to make handles" and adds that "Today, most available rubber is synthetic."
The product data's Handle row may say rubber, rubberized, TPE or TPR, and the makers explain only some of those words. TPE appears in a polymer maker's own words: Kraton, a maker of styrenic block copolymers, calls those polymers "a class of thermoplastic elastomers" and writes of "thermoplastic elastomer (TPE) compounds," and IUPAC's Gold Book defines an elastomer as a "Polymer that displays rubber-like elasticity." Case's handle key groups "Smooth Black Synthetic or Thermoplastic Rubber" under its code 2. No maker or standards page cited here defines the letters TPR, so this entry leaves them as printed.
A Handle row that says rubber cannot show whether the rubber is the whole grip or a layer over another material; the handle scale entry shows how spec lines name the parts of a grip.
Grip is where the makers make their case for rubber, each in its own words. Buck says "Rubber, Micarta and textured handles provide a superior grip in wet conditions." Kershaw describes its Trac-Tec inserts as "A rough-surfaced rubber insert that provides additional friction." Gerber describes one of its knives as "an injection molded frame with a rubber overmold handle," with the frame in glass-filled nylon, one of the glass-reinforced nylons the FRN (fiberglass-reinforced nylon) entry covers.