Bananas: Dry ripe but still firm bananas cut 1/8"" thin.
Guavas: Cook fruit in small amount of water with sugar to taste (or pressure) until soft enough to mash or sieve. Drain juice and set aside. Sieve, mash, or blend fruit until smooth. Spread on well-greased trays in about 1/8"" layers spread very evenly. When dry it should peel off tray easily using a knife or spatula dipped in boiling water (if necessary), and gently eased under fruit.
To reconstitute fruit: Soak about 2 hours in hot water. For pureed fruit, pour boiling water over and soak for 1/2 hour. Bring to boil for 1 minute until it becomes a thick sauce.