[I’ve substantially updated this article recently to answer some emailed questions about bento accessories and so on, so here it is again for your reading pleasure. Originally posted in August 2008.]
I recently got an email from a Just Bento reader concerning the plastic used to make bento boxes. She was concerned, since she couldn’t read the Japanese writing on the packaging. I’m sure a lot of other readers have similar concerns, especially given recent scares reported in the media about plastic containers leaching chemicals into food and beverages. Keeping in mind that I am not a scientist or expert, just a concerned consumer just like you, here’s what I’ve been able to find out by doing some research on various Japanese as well as English-language web sites.
The parts of plastic bento boxes that touch food from known Japanese manufacturers are generally manufactured using three types of plastic: polyethylene terephthalate (PET), polypropylene (PP), or a compound of PET and acrylonitrile butadiene styrene (ABS) called PET-A. A common practice is to use PP or PET-A for the bento box body and outer lid, and polyethelene for the flexible inner lids, or the main lids on small side boxes.
For example, the cheaper bento boxes made by Nakano Co.  (manufactured in China), which includes popular brands like Puti Fresh, Lube Sheep and Clickety-Clack that are sold at Daiso and similar ‘100-yen’ stores (previously ), are made of PP. According to The Green Guide  ( a site that is owned and operated by National Geographic), PP is a safe plastic, though it’s not very recyclable.
Higher end plastic bento boxes such as the very popular ones models made by Hakoya aka Tatsumiya Shikki  or Yellow Studio  (mostly manufactured in Japan, some accessories manufactured in China), use mostly PET or PET-A. (Hakoya also uses other plastics on parts of their boxes that aren’t in direct contact with food.) According to The Green Guide list, the main objection against PET seems to be the porous nature of the plastic, so it’s not recommended to re-use thin PET water bottles. However, from reading some Japanese reports, PET-A in particular seems to be regarded favorably as a recyclable yet food-safe plastic. In practice, I do find that my Hakoya and Yellow Studio bento boxes are easier to keep clean and of a better finish than my Lube Sheep boxes. (Update: As of late 2009-early 2010 I’ve stopped using any of my Lube Sheep boxes…not because of safety concerns, but just because they do tend to get a bit beat-up looking with continuous use. Well what can you expect from boxes that retail for 100-200 yen ($1-2 or so) in Japan?)
The substance that has generated the most controversy and concern in recent years when it comes to plastic food containers is bisphenol-A, or BPA. This exists in polycarbonate, a clear plastic that is used for some water bottles, as liners in metal cans, and so on. None of the major Japanese bento box manufacturers use polycarbonate in parts of their plastic bento boxes, water bottles and so on that touch food. (I have seen a few thermal mugs that use polycarbonate on the exterior parts that do not come into contact with the liquid.) It may be interesting to note that the Japanese canning industry began to voluntarily cut down on the use of BPA as can liners as early as 1998 (a decade before BPA even began to be talked about the the United States for example), and have been using other plastics since. (see .)
So in a nutshell, any bento box from a reputable Japanese maker should be perfectly safe. Generally speaking, food safety regulations in Japan are just as strict as they are in North America or Europe.
However, you should always heed the directions about whether or not a box is microwave-safe/dishwasher-safe or not. If you are not sure and are concerned, ask the seller of your bento box, or just don’t put it in the microwave. Needless to say, plastic is not oven or stovetop safe!
(Studies on the safety or not of BPA, especially for adults, still seem to be inconclusive. As with any other health related news, try to read as many reputable studies as you can and keep an open mind.)
Most rigid plastic bento accessories made by companies like Torune  such as picks, are made of ABS and/or polystyrene. Many reusable inner cups are made of silicone. Flexible plastic items such as baran (dividers, like ‘sushi grass’) made by Torune are made of PET.
Note that most of these accessories (except for silicone cups) are not microwave safe, so use your cute little picks and such for bentos that you don’t intend to nuke, or else take them out before doing so.
Nori cutters made by Arnest  (the Niko Niko Punch line) and Kaijirushi  (the Chuboos line), are made of ABS (the body) and zinc or a zinc alloy (the cutting parts). I do not have information on repurposed cutters that are meant for use on paper and other non-food products. If you’re really concerned about safety you may want to avoid using these on food.
Food cutters by Arnest (e.g. the Kyarappa line) are made of polystyrene.
It might be tempting to re-use takeout containers, but again according to The Green Guide, that may not be such a good idea  (this link is now broken, and their internal search leads back to their home page. grr). In essence you should not be re-using plastic containers that are not meant for multiple use, like takeout boxes and such, if you’re concerned about plastic safety.
The most practical alternative to plastic for bento boxes is probably stainless steel. See Stainless steel bento boxes . My favorite model of stainless steel bento box has a silicone sealing element around the inner rim of the lid; this is quite acceptable to me as a ‘green’ bento box, and makes it very practical. There are also 100% stainless steel bento boxes or lunch boxes, such as those from Lunchbots  (their orange-lid model is a good size for a bento box). Beware of packing any moist food in them since the lids are not leak-resistant.
Stainless steel bento boxes are generally more expensive than plastic, but should last a lot longer with proper care.
A very stylish though rather high maintenance alternative to plastic is wood. Traditionally bento boxes were made of wood, either untreated or coated with lacquer. Wooden bento boxes are wonderful, but need to be handwashed carefully and dried with a soft cloth immediately after washing. A famous type of wooden box is the Magewappa , made of uncoated bent Japanese cedar.
This is my personal opinion, but when it comes to wooden bento boxes, you really get what you pay for. Avoid cheap wooden boxes - these usually have a rough finish, inferior workmanship, and are generally rather nasty. Expect to pay at least $40-50 or more for a good wooden bento box. A genuine Magewappa bento box will cost you at least 6,500 yen (around $70) and on up from reputable stores in Japan. On the other hand, a high quality wooden bento box will last for years with proper care.
(Update added 1/09: All of the links in this article to The Green Guide site  are broken because they have changed them all apparently without proper redirects. What’s worse, their internal search results lead right back to the home page too. As a web developer myself I have to say this is so very lame. Anyway, once you get to their site (all links just go to their new front page) you can look around for the appropriate information. This page regarding Bisphenol-A (BPA)  is current, as of now, unless they change things around yet again.)
(Update added 2/10: Added link to Rubbermaid BPA page; added bento accessory information and plastic alternatives section.)