Table 2.

Characteristics and approximate composition of the different cell wall layers of flax fibers.

Cell wall layer	Average thickness	Microfibrils orientation	Approximate composition
PW	0.2 μm (Bos and Donald, 1999)	disperse orientation, preferentially 0° (Cosgrove and Jarvis, 2012; Rihouey et al., 2017)	∼25–40% Cellulose ∼30% Hemicelluloses (mainly xyloglucan and lesser amounts of arabinoxylan) ∼30% Pectins (mainly homogalacturonan; possibly rhamnogalacturonan (RG) I; RG II and arabinogalactan) (Carpita and Gibeaut, 1993; Andème-Onzighi et al., 2000; His et al., 2001; Morvan et al., 2003; Cosgrove and Jarvis, 2012; Mellerowicz and Gorshkova, 2012)
S1	0.5 μm (Domenges and Charlet, 2010; Bourmaud et al., 2013)	60–80° (Barnett and Bonham, 2004)	∼30–50% Cellulose ∼30% Hemicelluloses (xylan, xyloglucan) ∼5% Pectins (homogalacturonan and RG I) ∼10–20% Lignin (Gorshkova et al., 2010a; Cosgrove and Jarvis, 2012; Mellerowicz and Gorshkova, 2012; Rihouey et al., 2017)
G	Up to 15 μm or 90% of the total cell wall area at maturity (Morvan et al., 2003; Gorshkova et al., 2018)	8–10° (Bledzki and Gassa, 1999; Bourmaud et al., 2013)	∼75–90% Cellulose ∼15–20% Hemicelluloses (glucomanan) ∼5–10% Pectins (RG I) (His et al., 2001; Morvan et al., 2003; Mellerowicz and Gorshkova, 2012; Rihouey et al., 2017; Gorshkova et al., 2018)
Gn	0.5–1 μm through thickening (Bourmaud et al., 2013; Arnould et al., 2017)	Loosely packed as a heterogeneous structure (Roach et al., 2011)	Cellulose Hemicelluloses (glucomanan) Pectins [nascent RG I (i.e., long galactan chains)] (Gorshkova et al., 2010a, 2018; Roach et al., 2011; Rihouey et al., 2017)