Sounds like filter paper to me (usually a circle of the paper).
it is called a net
The net of a 2 dimensional shape can be folded into a 3 dimensional shape
A 2-D pattern folded to form a polyhedron is called a "net." Nets are flat representations of a three-dimensional shape that can be cut out and folded to create the polyhedron. Each net corresponds to a specific polyhedron, showcasing its faces and edges in a two-dimensional format.
The net of a 3D shape
The line that separates a shape into two matching halves is called the line of symmetry. When a shape is folded along this line, both halves mirror each other perfectly. In geometric figures, this line can be vertical, horizontal, or diagonal, depending on the shape's orientation.
It is a glass funnel into which can be placed a circle of folded filter paper (so that it too is the shape of the funnel) liquids may then be poured into the funnel and while the liquids will drain through (to be collected at the base of the funnel), any solids will be retained on the paper.
Filtration by use of a filter funnel is a method used to filter solid particles from a liquid substance. Filter paper must be folded and fashioned into a cone shape and placed inside a funnel in order to begin the scientific process of filtration.
It is a glass funnel into which can be placed a circle of folded filter paper (so that it too is the shape of the funnel) liquids may then be poured into the funnel and while the liquids will drain through (to be collected at the base of the funnel), any solids will be retained on the paper.
A tornado is called a funnel because of its shape - it often appears as a rotating column of air that narrows towards the base, resembling a funnel or a cone. This funnel shape is created as the tornado draws in debris and moisture from the ground, giving it its characteristic appearance.
To prepare a filter paper for filtration, first fold the filter paper in half and then in quarters. Next, open the filter paper to form a cone shape and place it in the filter funnel. Wet the filter paper with a small amount of the solvent being used for filtration to help it adhere to the funnel.
tornado clouds
it is called a net
A violent windstorm that often takes the shape of a funnel is called a tornado.
Funnel-shaped
If it is folded out it is called a net. It forms two circles and a rectangle.
A funnel shape
cone