A sponge is a tool

Tool

A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...

, implement

Implement

Implement may refer to:* Implementation — the process for putting a design, plan or policy into effect.* A class of tools — such as farm implements or writing implements....

, utensil

Tool

A tool is a device that can be used to produce an item or achieve a task, but that is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tools that are used in particular fields or activities may have different designations such...

 or cleaning aid consisting of porous material. Sponges are used for cleaning impervious surfaces. They are especially good absorbers of water and water-based solutions.

Sponges are commonly made from cellulose

Cellulose

Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....

 wood fibres, or foamed plastic polymers. Some natural sponges are still sold for the same purpose, although most natural sponges are now used either as body/facial sponges (bath sponges) or as decorating tools used for sponge painting.

There are three other categories of available synthetic sponges, low-density polyether (known as the rainbow packs of non-absorbent sponges), PVA (very dense, highly absorbent material with no visible pores) and polyester.

Polyester sponges are also sub-divided into a variety of types, some being reticulated (artificially broken-in) for ease of use. Other types are double-blown polyester, meaning that they have a high water retention ability, approaching or equalling PVA, but with visible pores and more flexibility of applications.

Harboring bacteria

Cellulose sponges (because they are primarily made of wood) can serve as a medium for the growth of harmful bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 or fungi

Fungus

A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

, especially when the sponge is allowed to remain wet between uses. Some manufacturers treat sponges with anti-microbial toxins to prevent this.

Bug Sponge

The 'bug sponge' was the brainchild of Ian Harold Brown of the 3M

3M

3M Company , formerly known as the Minnesota Mining and Manufacturing Company, is an American multinational conglomerate corporation based in Maplewood, Minnesota, United States....

 labs in St Paul, Minnesota. This sponge featured rigid polyether reinforced with an abrasive and hard-wearing polyethylene

Polyethylene

Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

compound to effectively remove dried-on insect residue from vehicle windshields. Since its introduction in 1974, the bug sponge has been one of 3M's least known success stories.