1. Which shoes are prohibited to be worn on Tisha B'Av?
Shoes made of leather.
2. What if only a small part of the shoe is made of leather?
This is also forbidden, whether the leather is found in the sole, the upper part of the shoe or just in the straps.
3. What if the shoes are imitation leather but look like real leather?
According to some opinions, this is also forbidden because of marit ayin -- one may not do an act that gives the impression to others that a prohibition is being done.
4. May one wear comfortable sports shoes etc.?
According to some opinions, such shoes should not be worn. The reason why we do not wear leather shoes is as an affliction and a discomfort, and therefore such footwear is inappropriate. It is praiseworthy to try to follow this opinion and limit oneself to thin-soled shoes that do not offer such comfort.
5. May one place a leather insert or foot support into the shoe?
If the insert is left in the shoe permanently, then it is considered part of the shoe and is forbidden.
If the insert is sometimes removed, it may be used on Tisha b'Av.
6. What if one is required to wear leather shoes for medical reasons?
Strictly speaking this is permitted. However, since many synthetic materials are available, one should try to obtain an alternative to leather if possible.
7. Are children allowed to wear leather shoes?
Strictly speaking, children below bar/bat mitzvah are permitted to wear leather shoes. However, it is customary to train children to wear other footwear from the age of two or three.
8. Why is it forbidden to sit on a chair on Tisha B'Av?
A mourner during the week of shiva may not sit on a chair. On Tisha B'Av we are all mourners over the destruction of the Temple.
9. When does this restriction apply?
From the commencement of the fast until halachic noon on Tisha B'Av. After noon, one may sit on a regular chair.
10. Must one sit directly on the floor?
If possible, one should sit on the floor, but it is permitted to sit on a pillow or cushion. According to some opinions, one should not sit on the bare floor.
If this is too difficult, one may sit on a low chair or stool.
11. How low should the chair be?
According to most opinions it should be less than 12 inches high (30cm). According to some opinions, one may use any chair that is lower than usual, irrespective of its height.
A person who is unable to sit on a low chair may sit on a regular chair. This includes sick or elderly people, and pregnant or nursing mothers.
12. What if a person is traveling?
It is permitted to sit normally while traveling (e.g. in a car, bus, etc.). According to some opinions, it is praiseworthy to stand if possible.
13. Is there any restriction about sleeping in bed?
A person should deprive himself of some comfort when sleeping on the night of Tisha B'Av. For example, if he usually uses two pillows, he should remove one. If he usually uses one pillow, he should sleep without it. Some have the custom to place the mattress on the floor, and some place a stone under the pillow or mattress.
14. What if this is too difficult?
People who are weak (and pregnant women) are not required to make such changes. Similarly, if these changes will prevent a person from sleeping, he may sleep as usual.
15. Are there any other restrictions to pleasure?
A person should refrain from all pleasurable activities on Tisha B'Av. For example, one may not go for a stroll, read a newspaper, or listen to the radio.
Excerpted from "Guidelines" - over 400 commonly asked questions about the Three Weeks (Targum/Feldheim).