Banana growers commonly use blue sleeves to protect the bunches during fruit growth. The Katryx(R) bag is a transparent sleeve with specific UVb and IR permeability properties, particularly a 30 % IR permeability reduction. This three-layer product was developed and patented by the Plastibana company, to allow better light and temperature conditions for banana growth. The effects of Katryx(R) and blue sleeves on the inside microclimate and on fruit quality were investigated. When using a frame to simulate the bunch, it was found that the Katryx(R) sleeve had a buffer effect with high temperatures. Thermal variations between night and day were thus limited; the inside temperature was kept around the theoretical optimum growth value in the West Indies, which varies between 29 and 30'C. When using the Katryx(R) sleeve, an increase in light quantity and a modification in light quality were also observed and, therefore, an increase in the photothermal coefficient. Banana plants ('Cavendish' cv 'Grande Naine') were used to investigate the effect of Katryx(k and blue sleeves on fruit growth. Katryx(R) covering increased fruit firmness and peel hardness, as well as fruit length and average grade (+2 to 8%), depending on the environmental conditions and on the position of the hand.