Excelsior is a wood product made of fibers from the Aspen tree, used in packaging, cushioning, stuffing of stuffed animals, and for the cooling pads in home evaporative cooling systems known as swamp coolers.
Excelsior, dyed green, makes an annual appearance as the "grass" in Easter baskets, or did in earlier decades before the prevalence of plastics.
In North America the term excelsior is sometimes used more generally, for any clean, loose material for shipment-packing of boxes or crates, such as styrofoam packing peanuts.
Excelsior is also used, banded into bale form, as archery backstops, comparable to how a straw bale would be used. If protected from the elements, it can last for many years. As locations wear, through repeated targetting, the bale can be dampened, such as from a running hose, and soaking it liberally. It expands and holds the water, just like a dry sponge would.