Futon covers are made for two essential uses. Firstly as a "bag" that has various layers of filling inserted. This is finally for use as a mattress casing by buttoning or tufting the futon cover.
When a futon cover is in use as a mattress casing the textile is probably Cotton Drill. Quality is variable but specialists use 100% cotton drill, most noteworthy because of inherent durability.
A cheap futon mattress will have a polyester type fabric or similar.
Removable futon covers
In North America and mainland Europe a detachable futon cover is seen as essential. The benefit of a futon cover that has a zip is easy removal or to put on. The use of a quality cotton drill enables the cover to have a machine wash on a low temperature.
Textiles and Colours
Most noteworthy, cotton drill is easy to dye so there is often a choice of colours. Other textiles that are in use include cotton chenille.