3D weaving is signified as a multiple-weaving method. Langer attempted to make a woven shell out of loom using a simple principle in the early part of the nineteenth century [7] . However, until today, there has been a lack of automated processes and machines for 3D-shaped shells [8] . In modern days, Computer-Aided Design (CAD) and various simulation programs have broadened new avenues for 3D shell manufacturing techniques. Buesgen introduced a revolutionary shape weaving to make 3D woven thin shells using Jacquard weaving [9] . The main idea of shape weaving is to create a fabric area having a larger spacing of weft and warp-ends than in the encircling fabric, which is achieved by mechanical devices and weave design. Shape weaving offers a programmable take-up mechanism to realize varying take-up lengths individually, which enables weft spacing variation. A Jacquard head is placed to execute shedding according to geometry requirements. The overall elements can be controlled by basic hard- and software for machine operation. Figure 1(a) shows a part of the loom used for shape weaving and Figure 1(b) illustrates a contoured shell produced by it [9] .

Loom is the pioneer of all weaving methods for 3D woven structures and shells. Greenwood patented a weaving loom to assist in making woven shells [10] and in the same year, Fukuta et al. showed a method and loom to make woven shells [11] . Talavasek and Svaty introduced a shuttle-less weaving machine [12] , and Krauland Jr. presented a method and apparatus for continuous woven structures [13] . The year 1991 to 2001 was the revolutionary period of making multilayered woven 3D structures, either as woven reinforcements for composites or woven 3D shells for automotive parts [14] - [25] .

Chen and Tayyar employed an add-on device (easy-to-use) to the conventional loom for making woven 3D shells [26] . They made changes in the let-off mechanism and used a profiled take-up roller. When the add-on device is removed, the loom resumes its original setup for making 2D shapes. Bhattacharya and Koranne introduced a novel method for 3D-shaped woven structures, but those are not of shell types [27] .

Chen et al. addressed different weaving techniques for 3D-shaped shells [28] . Jetavat showed a near-net-shape structure by 3D weaving [29] . Khokar demonstrated a method and apparatus to produce woven 3D profiles, which are primarily not shell structures [30] . Lu et al. described a novel Origami method to make a 3D woven box [31] . Lüling and Boussu et al. explained a few techniques to create 3D-shaped structures and their applications in their publications [32] [33] . A Ph.D. candidate at Technical University Dresden (Germany) made complex 3D shells Figure 2(a) using Jacquard technology and won the AVK-Innovation Prize 2022 [34] . Harvey et al. made a woven shoe Figure 2(b) by realizing different samples of experimental 3D woven structures [35] . They divided the warp into three distinct zones for design: sole, insole, and upper. They planted materials and yarns of varied sizes to emphasize the shoe’s center and bulk up the heel of the shoe so that different sizes of weft were possible to insert. They took the benefits of Jacquard weaving to finalize the traditional shoe components as part of their visual design. They employed the Weavecraft software to design 3D weaves effectively as it contains three easy-to-use windows that collectively provide the information. The task of the software is to generate a standard 2D binary file to run the Jacquard process, which converts into JC file language to run the loom [35] .

Thin shell preforms made by knitting technology represent a group of materials with great flexibility mainly due to the advantage of having fewer process steps. Flat knitting machines are mostly used for their design variability and it offers a versatile way to produce complex 3D-shaped shells, spacers, tubes, and other forms [36] . New software design, performance modeling, and new-generation machines capable of producing complex structures can stimulate the development of 3D-knitted preforms [37] .

The technologies from SHIMA SEIKI and STOLL have undertaken many important developments. Ciobanu produced a knitted shell Figure 3(a) using STOLL (CMS 320 TC) knitting technology and described it [37] . Dome-like structures with minimal or no seams can be produced by suspended stitches Figure 3(b) through WholeGarment^®, referred to as WG technology from SHIMA SEIKI [38] . The way of producing 3D knitted shells by suspended stitches using SHIMA SEIKI technology is also called the Spickel process.

There has been a lack of consistency in the lifetime of a car seat for a long time and woven 3D shell dominates automotive sectors. However, SHIMA SEIKI launched an anatomically contoured seat Figure 4(a) in cooperation with two German companies Trevira and imat-uve [39] . SHIMA SEIKI showed a prototype of a multiaxial knitting machine at Techtextil Fair (Frankfurt, Germany), which can create 3D-shaped shells as shown in Figure 4(b) and Figure 4(c) [40] . Simonis et al. made 3D-shaped knitted shells using a large circular knitting machine Figure 5, where needle parking or pendulum function was not followed due to the discontinuous movement, and continuous movement was maintained throughout the process [41] . Some key innovations for knitted shells were revealed at ITMA 2019 [42] .

The nonwoven process to make a 3D thin shell preform is unlike 3D weaving and 3D knitting. However, this process is shorter, faster, and more economical compared with other traditional ones [43] . The maiden 3D nonwoven shell is arguably the felted hat [43] . Felting is an easy process to realize and make 3D-shape manually, but the main drawback is productivity. The German company—Freudenberg Performance Materials developed nonwoven-based Lutraflor^® technology for automotive interior parts Figure 6(a) with excellent formability [44] . Air-laying nonwoven process is also an option to produce thin shells; the University of Manchester used a thermal-through air bonding system to make a softer shell preform Figure 6(b) and can be pressed by molds [43] . The engineers and researchers of ITM (Dresden, Germany) developed the net shape nonwoven (NSN) technique, where they used solid free forming (SFF) to process textile fibers into 3D nonwoven scaffolds Figure 6(c) without any negative mold or forging dies [45] .

Miura and Hosokawa showed 3D-shaped nonwovens using an electrochemical process [46] . Yin et al. combined melt-blown and spun bond processes to produce 3D nonwoven shells [47] . Dong described techniques and opportunities for 3D nonwoven shell preforms for the automotive industry [48] . Additionally, several informative publications have been reported on various aspects of 3D nonwoven preforms [49] [50] . However, not all these inventions and methods are suitable for technical yarns, which means depending on the product and demand one chooses the manufacturing technique.

Few unconventional methods like winding and/or layup processes have no convincing accomplishments in 3D thin shell textile preforms. Rolincik introduced the autoweave process, which was interpreted as 3D weaving [51] . Figure 7(a) shows one schematic diagram of the autoweave process. However, no images of the final product of the autoweave process are available so far. Khokar invented a noobing process, where no interlacement of fibers was recorded [52] . Khokar classified noobing process as a nonwoven 3D fabric-forming process and the final product of it was termed as noobed fabric but wrongly assumed 3D woven fabric. Moreover, the author classified noobing as a layup process according to the details and graphics available for it Figure 7(b) [52] . Khokar and Peterson revealed a noobing device [53] , although it is arguably not suitable for 3D thin shells. Nevertheless, a layup process like noobing can produce 3D-shaped forms [54] . Apart from autoweave and noobing, it has been reported that 3D thin shells are made using filament winding.

Filament winding is an established simple process for producing parts like spherical, cylindrical, and other forms. Aerospace filament winding has become impressively effective for contour parts at a premium price. It can be useful for making 3D thin shell preforms as shown in Figure 7(c) [55] . However, the productivity of the process depends on machine parameters like axis speed, preform geometry, and fineness of the fiber. Hopmann et al. presented a new winding strategy, which offers good productivity with reasonable costs [56] . McIlhagger et al. described filament winding and its manufacturing processes [57] .

The ability and advantages of 3D thin shell textile preforms contribute to reducing composite component manufacturing costs. It is possible to make suitable 3D thin shell preforms using appropriate technology with greater automation Table 3 illustrates the gaps between 3D thin shell manufacturing techniques and industrial requirements. It is not easy to discuss all limitations in one combined work to overcome the commercial hurdles. Therefore, continuous research and development are necessary to seal their place in the fields of technical textiles.

One of the most critical issues in the composite industry is to reduce weight by replacing heavy metal components. It has been reported that 50% - 75% weight reduction for some components is possible in the long term through carbon fiber-reinforced composites [4] . However, the absence of commercially available computational modeling and lack of automation in the processes are still major challenges for manufacturing 3D thin shell preforms. Three-dimensional thin shell textile preforms can be as lightweight components and they will add benefits to the automotive industries by optimizing fuel consumption. To succeed significantly with this mission, it is important to understand their long-term application requisites, replaceable opportunities with other 3D textile preforms, cost-effectiveness, the demand of consumers, and productivity. Table 4 presents a few important examples of possible 3D thin shell preforms with existing demands and requirements.