The author’s statement, “covers him entirely,” indicates that this garment must be thick enough that the skin cannot be seen through it. If the skin is visible through it, then it is insufficient.
The evidence that this is obligatory is that, regarding the Companions whose garments were too short to shroud them fully, the Prophet, peace and blessings be upon him, “commanded that the shroud be placed from the head, and that something of idhkhir be placed over the feet” (1). It is a well-known plant.
If nothing is available—for example, if he has been burned along with his clothes and no garments can be found in which to shroud him—then he is shrouded in grass or something similar, placed over his body and secured around it with bindings. If nothing at all is available, he is buried as he is, due to the general import of Allah’s saying: “So fear Allah as much as you are able.” [al-Taghabun: 16]