The MWS is a traditional Kydex insert similar to the ESSTAC KYWI.
The MWS is composed of 2mm shaped Kydex, with swatches of hook Velcro on its external faces. For best results, these should be affixed to corresponding Velcro loop within the pouches used. There’s a hole in the base of the insert, for drainage (if you have a pouch with a corresponding drainage grommet).
GM Tactical describes its insert as straightforward and it really is. Crucially, it’s a little cheaper than ESSTAC’s equivalent; it’s also available in OD and tan, as well as black.