What a good question! Rit loves hot water because it loosens the fibers in the fabric to accept the dye. We recommend using the hottest water safe for your fabric. However, if you want specific temperatures, here they are!

• If dyeing natural fabrics (such as cotton, linen, silk or wool), use Rit All-Purpose Dye at 140° to 160°F (60 to 71° C). If tap water is not hot enough, heat water on the stove and add to the dyebath.
• If dyeing a material that contains more than 35% synthetic material (such as polyester, acrylic or acetate), use Rit DyeMore for Synthetics at 180° to 220°F (82° to 104°C). To do this, you will need to dye with the stovetop method.