  We use a suite of high resolution molecular cloud simulations carried out
with the moving mesh code Arepo to explore the nature of star-forming
filaments. The simulated filaments are identified and categorised from column
density maps in the same manner as for recent Herschel observations. When fit
with a Plummer-like profile the filaments are in excellent agreement with
observations, and have shallow power-law profiles of p~2.2 without the need for
magnetic support. When data within 1 pc of the filament centre is fitted with a
Gaussian function, the average FWHM is ~0.3 pc, in agreement with predictions
for accreting filaments. However, if the fit is constructed using only the
inner regions, as in Herschel observations, the resulting FWHM is only ~0.2 pc.
This value is larger than that measured in IC 5146 and Taurus, but is similar
to that found in the Planck Galactic Cold Cores and in Cygnus X. The simulated
filaments have a range of widths rather than a constant value. When the column
density maps are compared to the 3D gas densities, the filaments seen in column
density do not belong to a single structure. Instead, they are made up of a
network of short ribbon-like sub-filaments reminiscent of those seen in Taurus.
The sub-filaments are pre-existing within the simulated clouds, have radii
similar to their Jeans radius, and are not primarily formed through
fragmentation of the larger filament seen in column density. Instead, small
filamentary clumps are swept together into a single column density structure by
the large-scale collapse of the cloud.
