Yes. That's why fat people can get into it.
Cotton or Linen
no it is not
T-shirt fabric is usually jersey knit. Made from cotton or poly/cotton and has a slight stretch.
Any sturdy, non-stretch fabric will do. A cotton broadcloth or even quilted cotton fabric will serve nicely. You probably could do the job by using a crib sheet.
Cotton fabric is breathable.
Because of the interaction of the tension in the vertical and horizontal fibers (warp and weft), the fabric produced is much less likely to stretch than for example a knitted or crocheted fabric. Take the difference between a cotton tee-shirt and a pair of cotton pants. The t-shirt is a knitted fabric and most likely cotton pants will be woven. You can easily tell how a t-shirt will stretch much more than the fabric of the pants.
Fabric cotton refers to cotton fibers used in the manufacture of woven cloth and other fabrics.
Cotton itself is not a stretchy fiber. Woven fabric is typically not stretchy. So no, I would not expect a cotton gauze to be stretchy unless it was a cotton blend.
Polyester is a material that fabric is fabricated from. Polyester can be knitted into fabrics that will stretch. Polyester also can be woven into fabrics that will not stretch. Polyester can be blended with other materials and fabricated into fabrics that will and will not stretch.
Why it is important to bleach cotton fabric
Cotton fabric is biotic because the cotton plant was once living.
A "knit" fabric will stretch, either side to side and/or up to down, but a "woven" fabric will not stretch.