Technology

Steel profile shapes: C vs U channel, Z, omega and custom sections

Author: Admin

September 27, 2026

Reading time 9 min.

Steel profile shapes used in industry include the C channel, U channel, L angle, Z section, omega (hat) section, closed tubes and T section, plus custom sections designed to a customer’s drawing. Each shape distributes material differently, so each one behaves differently under bending, torsion and buckling: picking the right section means reaching the stiffness you need with the least amount of steel.

This guide explains how each shape is built, where it is used, and when it pays to move to a custom profile made by cold roll forming. If you are new to the process itself, start with our guide on what cold roll forming is.

Steel profile shapes compared

The table summarises the most common sections produced by cold roll forming from coiled strip.

Shape	How it is built	Typical uses	Main advantage
C channel	Web and two flanges with edges turned inwards (lips)	Studs, purlins, frames	Stiffened flanges, high stiffness-to-weight ratio
U channel	Web and two straight flanges, no lips	Tracks, guides, edge and trim profiles	Easy to fit together with other profiles
L angle	Two legs at 90°, equal or unequal	Brackets, corner reinforcements, frames	Simple and cost-effective
Z section	Two flanges facing opposite directions	Roof and wall purlins	Can be lapped over supports for continuous spans
Omega (hat) section	Hat-shaped channel with two base flanges	Facade subframes, solar mounting rails, stiffeners	Sits flat on the substrate and offers a mounting channel
Closed tubes	Square, rectangular or round, HF welded	Frames, railings, load-bearing structures, furniture	Highest torsional resistance
T section	Flat flange and a web made by folding the strip onto itself	Ceiling grids, supports, stops	Double-thickness web with no welding
Custom section	Multi-bend geometry to the customer’s drawing	Industrial door tracks, racking uprights, window and door frames	Several functions in a single profile

C channel vs U channel: what is the difference?

In cold-formed steel, the difference is in the flange edges. A U channel has a web and two straight flanges. A C channel has the same web and flanges, plus lips: the flange edges are bent inwards to stiffen them. In framing, the U channel is often called a track and the C channel a stud.

The lips matter more than they seem. With thin cold-formed sections, the first limit is often not the strength of the steel but local buckling: under load, free flange edges tend to ripple. The lip stiffens the edge, so a C channel can carry the same load with a thinner gauge. That is why C channels are used as studs, purlins and load-bearing frames, while U channels work as tracks, guides and trims, wherever another element needs to slide in or sit inside.

L angle: the simplest shape

An L angle is made of two legs at 90°, equal or unequal. It is the easiest section to produce and to connect, and it is used for brackets, corner reinforcements, light frames, trims and stops. Its limit is low torsional stiffness: with heavy loads or long spans, a more closed section is the better choice.

Z purlin vs C purlin: when to use each

A Z section has its two flanges facing opposite directions, usually with stiffening lips. It is the classic shape for roof and wall purlins in industrial buildings.

The advantage of the Z over the C is lapping: two Z purlins nest into each other over the supports. The purlin becomes continuous across several spans, with less mid-span deflection and less steel per square metre of roof. The C purlin remains the better choice for single spans, for edges and openings, and wherever flat faces are needed for fixing.

Omega profile: the hat section

An omega profile, also called a hat channel, has a central channel and two side flanges that sit on the fixing surface. It is used as a subframe for ventilated facades and cladding, as a mounting rail for photovoltaic systems and as a stiffener for panels and sheet metal, including in automotive applications. The flanges spread the load on the substrate, while the channel provides a seat for screws, clips and accessories.

Profili in acciaio per la struttura di supporto di un impianto fotovoltaico su copertura industriale

Closed tubes: when torsion is the issue

Open sections (C, U, L, Z and omega) are efficient in bending but weak in torsion. When a profile has to carry eccentric loads or twisting forces, it needs a closed section. In cold roll forming, the strip is formed until the section closes, then seam-welded in line with high-frequency (HF) welding. The result is square, rectangular and round tubes, as well as closed sections with special geometries, for frames, railings, load-bearing structures and furniture.

Can a T section be cold formed?

Yes, with one trick. Heavy structural T sections are hot rolled or extruded in aluminium. In cold roll forming, a T is made by folding the strip back onto itself: the web is double thickness, with no welding, and the flange stays flat. This is the typical solution for suspended ceiling grids and for support and stop profiles, where low weight, precision and high volumes matter.

Custom sections to drawing

When no standard shape does the whole job, the answer is a custom section: a multi-bend profile that combines seats, stops, channels and stiffeners in one piece. Industrial door tracks, perforated racking uprights and many window and door profiles are custom sections.

The benefit is fewer operations and fewer assembly steps: one profile replaces two or three components and, with in-line punching, arrives already drilled and slotted. This is what our custom steel profiles to drawing are about.

How to choose between steel profile shapes

Four questions narrow down the choice:

How does the profile work? For bending about one axis, a C, Z or omega is enough; with torsion or eccentric loads, you need a tube.
How long is the span? Over several continuous spans, lapped Z purlins save weight; on a single span, a C is simpler to install.
How does it connect to the rest of the structure? Flat faces, base flanges or seats for other profiles point towards an L, an omega or a U.
Which secondary operations are needed? Holes, slots, bends and cut-to-length can all be done in line, so define them in the drawing from the start.

Material matters too: galvanized steel for outdoor use, stainless steel for aggressive environments or visible parts, aluminium where weight is critical. All options are on our page about cold-formed profile materials.

Standard shapes or a custom profile?

Standard catalogue sections such as IPE, HEA or UPN beams, or W and C shapes in the US, are hot rolled with fixed dimensions. The difference is explained in our guide to hot vs cold rolling. Cold roll forming starts from strip and gives the profile exactly the shape in the drawing. Sika works thicknesses from 0.4 to 4 mm and strip widths up to 550 mm, in carbon, galvanized, stainless and corten steel, aluminium and copper.

A custom profile pays off when volumes are recurring, when a standard shape forces you to oversize or add parts, or when you need tight tolerances and integrated operations. If you have a drawing, or even a sketch of the section, send it to us: our technical team will suggest the most suitable shape and thickness. See also our custom metal profiles.

Frequently asked questions

What is the difference between a C channel and a U channel?

In cold-formed steel, a C channel has lips: the flange edges are turned inwards, which stiffens the section and reduces local buckling. A U channel has straight flanges. C channels are used as load-bearing studs and purlins, U channels as tracks, guides and trims.

When should you use a Z purlin instead of a C purlin?

On multi-span roofs: Z purlins can be lapped over the supports to form a continuous purlin, which is lighter for the same load. C purlins are better for single spans, edges and openings, and wherever flat faces are needed for fixing.

Which profile shape has the best torsional resistance?

Closed sections: square, rectangular or round tubes. Open sections such as C, U, L and Z perform well in bending but poorly in torsion.

Can a T section be made by cold roll forming?

Yes, by folding the strip back onto itself: the result is a T with a double-thickness web and no welding, used for ceiling grids and support profiles.