[sandworm101]

Which is why in "fusion" bombs the majority of energy still comes from fission. The fusion reaction is a neutron source to boost the efficiency of the fission reaction. A pure fusion bomb, if one could ever trigger such a thing without fission, would not be very efficient.

[coldburst]

For "boosted fission" and early thermonuclear bomb designs yes, but not so for the more evolved thermonuclear designs. Navajo (Operation Redwing, 1956) was 95% fusion, Tsar bomba (1961) was 97% fusion, Housatonic (Operation Dominic, 1962) was 99.9% fusion.