1. Why an Empty Randoseru Feels Solid When You Lift It
When you lift an empty randoseru, it feels surprisingly solid. According to the Japan Randoseru Industry Association, as introduced by the Hokkaido Shimbun, the general weight of the main body is about 1.2 kg (2.6 lbs) for artificial leather models and about 1.4 kg (3.1 lbs) for natural leather models [4]. Since a 1-liter milk carton weighs about 1 kg (2.2 lbs), this is slightly heavier than that. Of course, these are "general values," and lighter models exist, but the numbers are not small. Why are they built so sturdily? A somewhat rough test provides a clue.
2. The 120 cm Drop Test: Did the Tablet Inside a Randoseru Survive?
The Industry Association conducted a test where they placed a 3 kg (6.6 lbs) load and a tablet inside the randoseru and dropped it from a height of 120 cm (about 47 inches) onto concrete, with the corner facing down. The result was that the tablet did not break only in the randoseru among the bags compared. In nylon or polyester backpacks, damage appeared on the screen after the third drop [5]. However, this test was conducted by the Association itself, and the conditions compared were limited. It is not evidence that "the randoseru is the strongest." Still, the results suggest that the concept of protecting contents through a lid and box shape works to some extent. So, how was this shape originally determined?
3. How the Randoseru Changed From a Military Satchel to a Box Shape With a Lid
The name "randoseru" is said to derive from the Dutch word "ransel," meaning a military satchel. In 1885 (Meiji 18), Gakushuin adopted the military satchel under the idea that "school supplies should be carried by oneself," which is considered the beginning [2]. Later, the Association's chronology states that the current shape drew closer after Ito Hirobumi gifted a box-shaped school bag in 1887. The shape and dimensions were standardized as the "Gakushuin type" around 1897 [2]. Current Association certification standards require the material to be leather or artificial leather, the shape to be vertical and box-shaped, and the lid (kabuse) to cover at least two-thirds of the whole. This is a standard set by the Association, not a law [1]. Why is the lid so large? No documents found this time clearly state the reason. We will look only at the facts of the standards and shape without deciding the reason. So, what is the construction inside the box?
4. The Hidden Hard Core Materials Inside a Randoseru
The outside of a randoseru is leather or artificial leather, but hard core materials are inserted inside. One manufacturer publicly states that they reinforce vulnerable parts with resin, wire, and double winding. They also use a U-shaped core material where three sides are integrated and doubled, measuring a maximum load capacity of 80 kg (176 lbs) [6]. This is one company's disclosure and is not a specification common to all randoseru. Still, it shows where effort is focused to achieve "lasting 6 years." Regarding shoulder straps, the Association explains that pressure is easily dispersed because they are fixed lower near the waist [5]. However, this is the Association's explanation. The standards also require free repairs for normal use over 6 years [1]. Durability seems supported by both "being hard to break" and "being repaired if broken." Now, does the lid relate to weight separately from this reinforcement?
5. How the Lid Affects a School Bag's Weight: Bags Without Lids Weigh About 750 g
The lid (kabuse) of a general randoseru covers the entire front and connects to metal fittings on the bottom. In contrast, another type of school bag that removes the lid and uses a zipper is introduced as weighing about 750 g (1.65 lbs) [7]. Since the general randoseru body is 1.2–1.4 kg (2.6–3.1 lbs), the type without a lid is lighter. It is explained that the construction of the lid relates to weight. However, the lid is not the only cause of weight. Materials and core materials are also involved, and these are different types of products, so a simple comparison is not possible. If the body weight has not changed much since the late Showa era, there may be other reasons for feeling it is "heavy." The next section looks at changes in textbooks.
Safety Note: Do not assume the lid is the only reason for the weight. Materials and internal structures also contribute.
6. Have Textbooks Become Heavier and Bigger? Page Counts, Sizes, and Government Notices
The weight of the randoseru body is explained as having hardly changed since the late Showa era. On the other hand, the page count and size of textbooks have changed significantly. According to data from the Textbook Publishers Association, in the 2005 school year, 96% of textbooks were B5 size. By the 2020 school year, large AB size was 40%, A4 size was 20%, and B5 size was 39%. The total page count for all subjects averaged 8,520 pages across 16 member companies, which is said to be 1.75 times that of 2005 [4]. The government is also aware of this issue. The Ministry of Education, Culture, Sports, Science and Technology issued a notice on September 6, 2018, titled "Considerations Regarding Students' Carried Items." It stated concerns that excessively heavy luggage could affect healthy physical development and introduced examples of schools allowing students to leave materials not used for home study in their desks [8]. This is a decision for each school and is not a nationwide obligation. The durability of the randoseru and the heaviness of the luggage seem to be separate questions.
7. How to Investigate Your Own School Bag's Weight at Home
Things you can do today: Use a kitchen scale to measure the weight of your own bag. Compare it empty and with today's textbooks. It does not have to be a randoseru; a regular bag is fine. Do not lift overly heavy loads beyond your capacity. Once you know the weight, look at where the heaviest items are and compare the page counts and sizes of textbooks. Stacking textbooks by size to visually see the difference between B5 and A4 is also interesting. Things you can do when out: Observe a randoseru being worn on the way to school from a distance to see how far the lid covers. Since these are other people's belongings, observe only, and ask permission before touching. Official information: Reading the Japan Randoseru Industry Association's certification standards page or the Ministry of Education's notice (PDF) allows you to verify the original wording of the numbers introduced in this article.