Traditionally, production was centered in Lüdenscheid, but diecast models are now made in China, the Philippines, Poland, Taiwan and Vietnam.

Founded in 1921,[1] Sieper-Werke (Sieper Works) was originally a manufacturer of metal tools and cutlery in zamak and aluminium; later on, it also made ashtrays, badges, medals, belt buckles, and buttons.

In 1943, it expanded to a facility in Hilchenbach, about 50 kilometres (30 mi) from Lüdenscheid (though the latter remained Sieper-Werke's headquarters), in which products like plastics, furniture, mirrors, and cabinets were developed and manufactured.

Its Lüdenscheid operations generally focused on promotional items for major brands, such as the 'elephant shoe' and 'Zeller black cat', which were injection-moulded.

By 1958, Sieper-Werke had dropped figures to focus exclusively on plastic vehicles, except where animals attended tractors and such.

[2] Several American cars were also offered, including a 1956 Buick Century, a 1957 Mercury Voyager station wagon, and a 1960 Chrysler New Yorker.

Different colors were also shown on the opposite panels; some boxes were blue and red, some green and yellow, and others orange and cream.

For some time, the illustrations of the vehicles on the boxes were bathed in a yellow light from the round sun-like Siku logo.

Super Series vehicles include unconventional sports cars like the Gumpert Apollo or the Wiesmann GT, heavy machinery (like forestry log loaders, piston bully snow tracked vehicles, an ultra-detailed stake bed Mercedes Unimog, potato digger truck), a triple-engined competition pulling tractor, modern tram and subway train cars, and even the AIDAluna cruise ship in 1:1,400 scale (18 cm long).

[1] After 2005, some of these realistic plastic vehicles, like a MAN refuse truck, were twelve inches long or more and, typical for the era, made in China, not Germany.

In 2004, a radio-controlled tractor was introduced in the new Siku Control line, which added play value in addition to the regular Farmer Series vehicles.

Through the 1980s, HO (1:87) scale manufacturers like Herpa, Busch, Trident, and Roco became more important in the European hobby market.

In 1984, Sieper-Werke moved to strengthen itself in this market with the purchase of Wiking-Modelbau, based in West Berlin and famous for HO scale plastic models.

The Club Series was introduced in 1990 and consisted of die-cast trucks and farm vehicles made in a smaller scale (usually 1:87).

This range of classic fire engines in 1:50 scale was added in 2005 to complement modern models in the Super Series.

Though the line is aimed primarily at outdoor play, with durability being a main feature, a level of detail and realism is still maintained.

With its respected V-Series, Siku battled with Majorette and Efsi for the European market, but became the diecast leaders in Germany.

Starting in the early 1970s, Siku entered international markets with increasing success, and the company abandoned most other diecast products, focusing more on vehicles.

[2] While Siku became well known across Europe, the brand never became widely popular in the United States, only sometimes being found at specialty hobby shops.

The American scarcity was despite offering American cars like the Buick Wildcat, Oldsmobile Toronado, Pontiac Bonneville convertible, Cadillac limousine, Pontiac GTO, Chevrolet Corvette, Lincoln Continental Mark III, Ford Mustang, and Ford trucks.

[6][7] As of 2010, Siku does not export toys to the United States due to conflicts with the 2008 Consumer Product Safety Improvement Act (CPSIA).

Today, new models still retain their quality similar to older Matchbox, Dinky and Corgi of decades past.