There are a few types of obi that you can wear with your kimono. Here, I will go over the basic types of obi and when you can wear them. This list goes from most formal to most casual.
Women's
Maru
Maru obi are sewn from one large roughly 62cm bolt of heavily woven cloth that is folded in half and sewn shut. The material is usually stiff and thick, and it features full patterning and embroidery along the whole length. These obi are almost always made with gold and/or silver threads and are very formal. They usually are no longer produced, but you can find many vintage pieces still being sold. These obi are usually around 4 meters long.
Maru Formality: Most formal, could be worn with a wedding outfit or possibly with kurotomesode. But most people keep them as display pieces these days.
Fukuro
Fukuro obi are a simplified version of the maru obi. They feature two different materials sewn together on the front and back. The obi is only pattern on one side and is much thinner than a maru obi. The width is generally 30cm and the length can vary from 3.5 to 4.5 meters long. There are two main types of patterning for fukuro obi.
Rokutsu - The obi has a pattern covering only 60% of the front, specifically the areas that will show once the obi has been tied. This is the most common type of fukuro obi.
Zentsu - The obi has a pattern covering the entire front face. These are less common and more expensive due to the obi requiring almost double the embroidery.
Fukuro formality: anything from crested iromuji and up, usually tied using the nijyuudaiko musubi
Maru
Maru obi are sewn from one large roughly 62cm bolt of heavily woven cloth that is folded in half and sewn shut. The material is usually stiff and thick, and it features full patterning and embroidery along the whole length. These obi are almost always made with gold and/or silver threads and are very formal. They usually are no longer produced, but you can find many vintage pieces still being sold. These obi are usually around 4 meters long.
Maru Formality: Most formal, could be worn with a wedding outfit or possibly with kurotomesode. But most people keep them as display pieces these days.
Fukuro
Fukuro obi are a simplified version of the maru obi. They feature two different materials sewn together on the front and back. The obi is only pattern on one side and is much thinner than a maru obi. The width is generally 30cm and the length can vary from 3.5 to 4.5 meters long. There are two main types of patterning for fukuro obi.
Rokutsu - The obi has a pattern covering only 60% of the front, specifically the areas that will show once the obi has been tied. This is the most common type of fukuro obi.
Zentsu - The obi has a pattern covering the entire front face. These are less common and more expensive due to the obi requiring almost double the embroidery.
Fukuro formality: anything from crested iromuji and up, usually tied using the nijyuudaiko musubi
Nagoya
The fukuro obi was further simplified in the 20th century into the Nagoya obi. Nagoya obi have the same width as the fukuro, 30cm thick. But the length is much shorter, usually only 3.5 meters long. There are three main types of Nagoya obi.
Nagoya shitate - This is the most standard type of Nagoya obi. The section of the obi that wraps around the body is stitched in half, so you don't have to fold the obi at all to put it on.
Matsuba shitate - Only about 30cm of the obi is stitched in half, to help get you started with folding. The rest is left fully open.
Hiraki shitate - This style does not stitch any of the obi in half, so the full length of the obi is 30cm wide.
Because Nagoya obi are usually not fully patterned and most are partially stitched closed, this limits what kind of knot you can tie. Generally people tie a taiko musubi or similar variant, such as the tsunodashi musubi.
Formality: Casual kimono, such as komon, up through iromuji with no crest.
The fukuro obi was further simplified in the 20th century into the Nagoya obi. Nagoya obi have the same width as the fukuro, 30cm thick. But the length is much shorter, usually only 3.5 meters long. There are three main types of Nagoya obi.
Nagoya shitate - This is the most standard type of Nagoya obi. The section of the obi that wraps around the body is stitched in half, so you don't have to fold the obi at all to put it on.
Matsuba shitate - Only about 30cm of the obi is stitched in half, to help get you started with folding. The rest is left fully open.
Hiraki shitate - This style does not stitch any of the obi in half, so the full length of the obi is 30cm wide.
Because Nagoya obi are usually not fully patterned and most are partially stitched closed, this limits what kind of knot you can tie. Generally people tie a taiko musubi or similar variant, such as the tsunodashi musubi.
Formality: Casual kimono, such as komon, up through iromuji with no crest.
Hanhaba
Hanhaba means half width. These obi are only 15cm wide along the whole length and are between 3 to 4 meters long. This is the standard choice of obi when wearing yukata, but more formal hanhaba obi made for kimono exist as well. Because they are half width, they cannot be used for the taiko musubi, and generally people tie these into fluffier, bow-like knots.
Formality: Komon or yukata only
Hanhaba means half width. These obi are only 15cm wide along the whole length and are between 3 to 4 meters long. This is the standard choice of obi when wearing yukata, but more formal hanhaba obi made for kimono exist as well. Because they are half width, they cannot be used for the taiko musubi, and generally people tie these into fluffier, bow-like knots.
Formality: Komon or yukata only
Heko
Heko obi are soft obi made from a thin and extremely wide single strip of cloth. They can be anywhere from 3 to 4 meters long and up to 70 cm wide. Originally, heko obi were only worn by children, as they are very comfortable and easy to tie. But they since became popular with men for yukata, and now more recently with women as well. Some traditional kimono enthusiasts may think heko obi is not appropriate for adults (or specifically women), but a growing movement of young people have been using them for both yukata and even casual kimono as well.
Formality: Yukata, or komon when done right
Heko obi are soft obi made from a thin and extremely wide single strip of cloth. They can be anywhere from 3 to 4 meters long and up to 70 cm wide. Originally, heko obi were only worn by children, as they are very comfortable and easy to tie. But they since became popular with men for yukata, and now more recently with women as well. Some traditional kimono enthusiasts may think heko obi is not appropriate for adults (or specifically women), but a growing movement of young people have been using them for both yukata and even casual kimono as well.
Formality: Yukata, or komon when done right
Men's
Kaku
Kaku obi are the same length as most women's obi, around 4 meters long. But they are much thinner, usually only about 10cm wide. They are the standard obi for all men's kimono and can be worn with yukata all the way up through 5 crest kuromontsuki at a wedding. The formality is entirely dependent on the pattern, material, and design. Commonly, they are made of a weave called hakata ori, but other styles are increasingly more common.
Heko
As mentioned above, heko obi are considered very casual. Men's and women's heko obi are roughly the same size, 3m to 4m long and up to 70cm wide. Generally only worn with yukata at summer festivals, or with kimono when worn at home.
Kaku
Kaku obi are the same length as most women's obi, around 4 meters long. But they are much thinner, usually only about 10cm wide. They are the standard obi for all men's kimono and can be worn with yukata all the way up through 5 crest kuromontsuki at a wedding. The formality is entirely dependent on the pattern, material, and design. Commonly, they are made of a weave called hakata ori, but other styles are increasingly more common.
Heko
As mentioned above, heko obi are considered very casual. Men's and women's heko obi are roughly the same size, 3m to 4m long and up to 70cm wide. Generally only worn with yukata at summer festivals, or with kimono when worn at home.
Children's
Shigoki
Shigoki obi are made of a soft, single piece of fabric that is tied at the bottom of or below the normal obi. Originally, they were used by women to tie up their kimono for going outside. But now they have become a standard part of the outfit for 7-year-old girls during shichi-go-san. They are usually lucky or youthful colors, such as red or bright green. They usually have tassels at the end and are purely decorative. Sometimes women will wear them as well for an extra flair of style.
Heko
The heko obi for children is exactly the same as men's and women's, but much smaller.
Shigoki
Shigoki obi are made of a soft, single piece of fabric that is tied at the bottom of or below the normal obi. Originally, they were used by women to tie up their kimono for going outside. But now they have become a standard part of the outfit for 7-year-old girls during shichi-go-san. They are usually lucky or youthful colors, such as red or bright green. They usually have tassels at the end and are purely decorative. Sometimes women will wear them as well for an extra flair of style.
Heko
The heko obi for children is exactly the same as men's and women's, but much smaller.
Less common obi types
Chuuya obi
Chuuya means day and night, and these obi have a bright and vivid patterned side, and a darker, more subtle side. Sometimes also called hara-awase obi, these obi are the same length as a Nagoya obi. This type of obi is not so common anymore, but you can still find them occasionally.
Chuuya obi
Chuuya means day and night, and these obi have a bright and vivid patterned side, and a darker, more subtle side. Sometimes also called hara-awase obi, these obi are the same length as a Nagoya obi. This type of obi is not so common anymore, but you can still find them occasionally.
Sanjaku
Sanjaku means 3 jaku or 37.9cm. These obi are roughly the same size as a men's kaku obi, but a little narrower. They are usually made from a soft, cotton-like material that is comfortable and easy to wear. These were popular with every-day people in the edo period, and you may still see them today used to tie closed festival jackets (happi) or worn at home to be more comfortable.
Sanjaku means 3 jaku or 37.9cm. These obi are roughly the same size as a men's kaku obi, but a little narrower. They are usually made from a soft, cotton-like material that is comfortable and easy to wear. These were popular with every-day people in the edo period, and you may still see them today used to tie closed festival jackets (happi) or worn at home to be more comfortable.
Tsuke
This obi have many names, tsuke obi, tsukiri obi, tsukure obi, or kantan obi. Tsuke-obi are simple to wear, two piece obi. Usually the knot that goes at the back and the section that wraps around the body are separated. The knot section is usually pre-tied, but it may also be loose to allow for tying different knots. It's very common to see these for yukata obi but plenty of taiko musubi for casual kimono exist as well.
This obi have many names, tsuke obi, tsukiri obi, tsukure obi, or kantan obi. Tsuke-obi are simple to wear, two piece obi. Usually the knot that goes at the back and the section that wraps around the body are separated. The knot section is usually pre-tied, but it may also be loose to allow for tying different knots. It's very common to see these for yukata obi but plenty of taiko musubi for casual kimono exist as well.
Hassun vs Kyusun Nagoya Obi
To further complicate the types of Nagoya obi, there are two more categories they can be divided into.
Hassun means 8 sun (about 24cm) and these obi are made of two pieces of fabric cut to 30cm and sewn together with no interfacing or stiffener inside. A more stiff fabric is used than with the kyusun Nagoya obi, but because of the lack of stiffener, the overall obi ends up being thin and more flexible. This gives it a more casual appearance.
Kyusun means 9 sun (about 27cm) and these obi are made of two pieces of fabric cut to 32-34cm to allow room for a stiffening material to be sewn into the center. Because this stiffener is used in fukuro obi as well, kyusun Nagoya obi look more similar to fukuro and stand up straighter. Therefore they are generally considered to be more formal than hassun Nagoya.
The majority of Nagoya obi are kyusun, but you can find some interesting hassun obi made from various fabrics.
To further complicate the types of Nagoya obi, there are two more categories they can be divided into.
Hassun means 8 sun (about 24cm) and these obi are made of two pieces of fabric cut to 30cm and sewn together with no interfacing or stiffener inside. A more stiff fabric is used than with the kyusun Nagoya obi, but because of the lack of stiffener, the overall obi ends up being thin and more flexible. This gives it a more casual appearance.
Kyusun means 9 sun (about 27cm) and these obi are made of two pieces of fabric cut to 32-34cm to allow room for a stiffening material to be sewn into the center. Because this stiffener is used in fukuro obi as well, kyusun Nagoya obi look more similar to fukuro and stand up straighter. Therefore they are generally considered to be more formal than hassun Nagoya.
The majority of Nagoya obi are kyusun, but you can find some interesting hassun obi made from various fabrics.