Wood consists of three components: cellulose, hemicellulose and lignin (see first picture).
Delignified, densified wood is a new way of modifying wood. As in the classical pulp and paper manufacturing process, all the lignin and a third of the hemicellulose are chemically removed from the raw material. The compression of the material leads to a folding of the cell walls.
Second picture shows the material change due to delignification and compaction (Frey et. al, 2018, p. 5030):
A). Natural untreated raw material wood: red = lignin, yellow = cellulose, blue = hemicellulose.
B). Delignification: Total lignin (red arrows) and 1/3 hemicellulose (blue arrows) is washed out, Cellulose remains, slight shrinkage of the structure.
C). Compaction: Cellulose framework is compressed by high force with lateral shear -> Hollow spaces are compacted.