Firkin,
A combination of materials depending on when the grip was made. The only "solid" metal grips I guarantee are pure metal are the scale type grips found on the Maharaja of Jodphur kukris of WW I and the rare M43 with an aluminum grip.
Most others seem to be metal over a wood core and very well done. I also have some WW II pieces that feel solid, but these were principally used by the pipes and drum unit rather then in combat. The bright metal handles were also used by police forces to make their kukris even more obvious. Most have a full length tang as indicated by the keepers at the pommel.
I have an early steel handled piece used by the Kubo Valley Police in Assam that has a brightly polished grip and a dark blued blade. A very sexy and good looking kukri from around 1870. I think this may be a solid grip with the tang running its length and with a diamond shaped keeper and peened over tip.
Then there is the question of Indian talwar handled pieces and kora style grips. Depending on age some are wood filled and some are solid. I know that's not very dfinitive, but it's the best I can do w/o making this a book chapter.
Finally there are the "engraved" kukri grips that come in a variety of metals including silver, brass and gold washed nickel. These usually have a wood base and the sheets of "engraved" work are wrapped around the core and expertly soldered together with a pommel cap being soldered on last. They are not engraved, but the sheet is pounded over a form and then detalied once they are attched to the core.
I will try to get a pix posted that shows a variety of the metal grips discussed.