Bread for the Mass

What kind of bread can be used at Mass?

Concerning the bread used for the celebration of the Eucharist, the General Instruction of the Roman Missal states:

By reason of the sign, it is required that the material for the Eucharistic Celebration truly have the appearance of food. Therefore, it is desirable that the Eucharistic Bread, even though unleavened and made in the traditional form, be fashioned in such a way that the Priest at Mass with the people is truly able to break it into parts and distribute these to at least some of the faithful. However, small hosts are not at all excluded when the large number of those receiving Holy Communion or other pastoral reasons call for them. (no. 321)

The Instruction Redemptionis Sacramentum gives a further description concerning the bread used for Mass:

The bread used in the celebration of the Most Holy Eucharistic Sacrifice must be unleavened, purely of wheat, and recently made so that there is no danger of decomposition. It follows therefore that bread made from another substance, even if it is grain, or if it is mixed with another substance different from wheat to such an extent that it would not commonly be considered wheat bread, does not constitute valid matter for confecting the Sacrifice and the Eucharistic Sacrament. It is a grave abuse to introduce other substances, such as fruit or sugar or honey, into the bread for confecting the Eucharist. Hosts should obviously be made by those who are not only distinguished by their integrity, but also skilled in making them and furnished with suitable tools. (no. 48)