1. How Sol Is Poured Into a Mold and Drained Out to Make Hollow Figures
Soft vinyl figures are hollow toys made from polyvinyl chloride (PVC). The material is called "sol," which consists of tiny PVC particles mixed into a liquid. When this sol is placed in a metal mold and heated, it becomes a semi-solid state called "gel" [1]. During this heating process, the mold is flipped upside down. The part near the mold walls forms a thin skin, but the center remains liquid. The unhardened sol is then poured out, leaving the figure hollow [1][2]. This is not a case of scooping out the inside; rather, the inside is removed before it can harden. Because the figure is hollow, less material is needed, and the toy becomes lighter. If the walls are made thinner, the toy becomes even lighter [4]. This lightness is ideal for toys that children hold and play with. So, how is the thickness of this skin determined? To remove the unhardened part, the mold is flipped, leaving only the wall layer behind [1][2]. By stopping the process and removing the inside, only the thin outer layer remains.
2. How Heating Time Changes the Thickness of the Figure's Wall
Factory descriptions explain that after putting sol into the mold, air bubbles are removed using vacuum or centrifugal force. The metal mold is then heated to create the wall. Afterward, the mold is flipped to return the excess sol, heated again for the final bake, and finally cooled with water before being removed [3]. The first heating stage greatly affects the wall thickness. Heating for a longer time makes the walls thicker, while a shorter time results in a thinner and lighter figure [4]. This is likely because the thickness of the hardened layer changes depending on the time it takes for heat to travel from the outside to the inside. Therefore, even with the same mold, changing only the heating time can produce either a thick figure or a thin, light one. The length of time acts as a dial for wall thickness. In one workshop’s example, the mold is dipped in an oil bath at about 190°C for approximately 2 minutes [2]. This is about 90°C higher than the boiling point of water (100°C). However, this is just one workshop’s example. Temperature and time likely change depending on the size of the figure and the material. These numbers should be read as rough guidelines.
3. How a Wax Prototype Gives the Mold Its Shape
The shape inside a soft vinyl mold begins with a prototype. The scales and facial wrinkles of a monster are carved into the inside of the mold because they are copied from the prototype. The craftsman who makes the prototype is called a master modeler. It is said that they often create the shape directly while looking at reference materials or samples [1]. The prototype is often said to be made of wax, which can be melted and removed later [1]. The general manufacturing flow is: prototype, wax mold, metal mold, test molding, mass production molding, and finally, trimming and painting [3]. Besides mass production using molds, garage kits sometimes use a method called "burning out," where the mold is broken to remove the contents [1]. The scales and wrinkles are shapes carved into the inside of the mold that appear on the outside of the wall when the sol hardens.
4. Trimming Flash and Painting the Figure After It Leaves the Mold
After the figure is removed from the mold, thin excess material protrudes from the seam. This excess is called "flash" and is cut away to tidy the figure. Then, the figure is painted, and if there are parts, they are assembled [3]. Painting is done by a specialist craftsman, different from the one who made the prototype. They spray special paint with an airbrush, blowing a dark color and wiping it off immediately. The dark color remains in the depressions, creating deep shadows [5]. The fine carvings copied from the mold become more visible through this shading. A figure is not complete just by being taken out of the mold; human hands decide the final expression.
5. How Soft Vinyl Replaced Flammable Celluloid as a Toy Material
Before soft vinyl, celluloid was used as a toy material. Wikipedia states that because celluloid is flammable, its use in toys was regulated, and soft vinyl began to be used as a replacement in the 1950s [1]. The specific law names and years of regulation are not written there. The first proper soft vinyl figure in Japan is said to be Masudaya’s "Milk-Drinking Doll" from 1954 [5]. A turning point for soft vinyl’s popularity was 1966. Marusan Shoten released soft vinyl monsters from "Ultra Q," which became a huge hit during the first monster boom. It is said that part of the manufacturing was entrusted to Shimada Toys, which had previously made cute animal soft vinyl figures [5]. This means the same hollow-making method was used, but the subject changed from animals to monsters. Materials are not fixed either. Plasticizers (chemicals that soften materials) like phthalate esters have been viewed as problematic, and thermoplastic elastomers have started to be used in some cases. However, this has not happened for all products [1]. Celluloid was regulated for toy use due to fire hazards [1]. The same manufacturing method was used, but only the subject matter changed.
6. Three Things to Check on Your Own Figure: Holes, Seams, and Weight
If you have a soft vinyl figure at hand, look for these three things. First, are there small holes on the head or soles of the feet that connect to the inside? Second, look around the body for a thin vertical line, which is the trace of the mold seam. Third, is the weight light for its size? If you do not have a figure at home, you can look at one in a toy store. Do not press hard, take it apart, or try to break it to look inside. If you want to know more, workshop pages that introduce the manufacturing process are available in Japanese [2][3]. Comparing the flow of processes in those pages with the order in this article may lead to new discoveries.