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
The net of a 3D shape
When a circle is folded along its diameter, it creates two congruent halves or semicircles.
If I understand your question, the shape would be "geometrical"
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.
tornado clouds
Funnel clouds
it is called a net
Funnel-shaped
A violent windstorm that often takes the shape of a funnel is called a tornado.
If it is folded out it is called a net. It forms two circles and a rectangle.
A funnel shape
A two-dimensional shape that can be folded into a three-dimensional figure is often called a net.
It is a tornado BUT it is funnel shaped NOT an "inverted funnel" The other rotating destructive wind phenomena is not part of a storm (they usually happen on clear, hot days) and is called a whirlwind.