What is the difference between Istisna and Salam?

The following are the main differences between Istisna' and Salam:

1. In case of Istisna, the subject on which transaction of Istisna' transaction is based is always a thing which needs manufacturing/assembling/processing etc., whereas in case of Salam, the subject matter can be a thing that does not necessarily need manufacturing etc.

2. The price in Istisna' does not necessarily need to be paid in full in advance. It is not even necessary to pay the full price at delivery. It can be deferred to any time according to the agreement of the parties. The payment may also be made in installments. In case of Salam, the price has to be paid in full in advance.

3. The time of delivery does not have to be necessarily fixed in Istisna' whereas in case of Salam the time of delivery is an essential part of the sale.

4. Istisna contract can be cancelled before the manufacturer starts the work. Salam contract cannot be cancelled unilaterally.