The word "tube" denotes a simple geometric form — a hollow cylinder — and a broad family of objects, systems and metaphors that share that shape or the idea of a conduit. Tubes appear as manufactured components (metallic pipes and polymer tubing), electronic devices (vacuum tubes and cathode ray tubes), biological structures (pollen tubes and vascular conduits), packaging (squeezable tubes for pastes) and cultural references (media names and slang). This article summarizes common types and uses, outlines key technical and historical points, and explains how the same underlying form performs different roles in engineering, nature and society.

Definition and basic properties

In geometry a tube can be described as a hollow cylinder or cylindrical shell defined by inner and outer radii and a length; as an engineering element it is characterised by cross-sectional shape, wall thickness, material and flexibility. Tubes may be rigid or flexible, seamless or welded, and manufactured from metals, polymers, composites or ceramics depending on the application. Basic properties that determine performance include tensile strength, corrosion resistance, thermal conductivity and ease of joining. Standards and specifications for tubing and piping exist internationally to ensure safety and interchangeability; engineers commonly consult documents from recognized standards bodies when selecting materials and designs.

Electronics and display technologies

Early electronic amplifiers and radios used vacuum tubes to control electron flow within a sealed envelope; these devices enabled amplification and switching before solid-state transistors became dominant. The vacuum tube remains important to collectors and some audio enthusiasts who value tube amplifiers for their characteristic sound. For display technology, the cathode ray tube was the standard for televisions and computer monitors for much of the 20th century, producing images by directing electron beams onto phosphorescent screens. Both kinds of tubes are distinct in function—one manipulates electrical signals, the other produces visible images—but both contributed crucially to early electronics and media devices.

Mechanical, plumbing and structural uses

Tubes and tubing serve as conduits for fluids and gases in plumbing, HVAC and industrial systems; flexible pneumatic tubing is used where motion and vibration occur, while rigid pipe and tube systems carry pressurised media. In transportation, inner tubes are inflatable components historically used inside pneumatic tires. In structural engineering the term "tube" refers to a building system in which the exterior frame forms a stiff, hollow tube that resists lateral loads from wind and earthquakes; variations of the tube concept have enabled the construction of taller and more economical high-rise buildings.

Biology, geology and natural occurrences

Nature produces tubular forms at many scales. In vascular plants, pollen tubes allow sperm cells to reach ovules during fertilization (pollen tube), while animal anatomy features many tubular structures such as blood vessels and digestive tracts. Geological processes create lava tubes where flowing molten rock drains away and leaves a hollow passage. In surf terminology the hollow, rideable part of a breaking wave is called the tube or barrel (hollow wave), illustrating how the word is applied both to solid conduits and to transient fluid shapes.

Packaging, consumer products and everyday language

Squeezable tubes are a common packaging format for pasty or viscous goods such as toothpaste, ointments and some foodstuffs; they protect contents from contamination and allow controlled dispensing. The tube format is valued for portability and convenience: single-serve and travel sizes are often made this way. Popular culture has adopted the term: a well-known online video platform is commonly referred to simply as YouTube, and band and show titles sometimes use the word to convey modernity or connectivity. In British English, "the Tube" is also a familiar informal name for an urban rapid transit system, showing how the same short term acquires locality-specific meaning.

Media, entertainment and memes

"Tube" figures in several media titles and names. Historic and contemporary uses include television programmes, musical groups, software titles and theatrical productions. The Blue Man Group used the title "TUBES" for one of its productions (Blue Man Group). The word also appears in internet culture: the expression "series of tubes" became widely known after being used as an analogy for the internet, generating discussion about metaphors for networks (analogy for the Internet) and giving rise to an internet meme (series of tubes meme). These examples show how a concrete physical concept often becomes a vehicle for metaphor in public discourse.

Manufacture, joining and maintenance

Manufacturing methods for tubes include extrusion, drawing, rolling and welding for metals, and extrusion and co-extrusion for polymers. Joining techniques vary with material and service: welding and brazing are common for metal tubes, while adhesives, heat fusion and mechanical fittings are used for plastics. Maintenance considerations include protection against corrosion, monitoring for fatigue and ensuring seals and joints remain leak-free. In critical systems such as gas delivery, medical devices or structural elements, strict inspection and testing regimes are applied to maintain safety.

Not all cylindrical objects are functionally equivalent: pipes are often specified for pressurised flow and follow dimensional standards for fittings, whereas tubes may be defined by outside diameter and wall thickness for structural or instrument applications. Hoses are flexible tubes designed for motion, and conduits may refer to electrical or communication pathways. Understanding the intended function—fluid transport, structural member, enclosure or conveyance of signals—helps clarify which term and which design are appropriate.