Rayon and spandex are both synthetic fibers. Proper care procedures vary. Howstuffworks.com states that following the instructions on a garment's care label is the best starting point to ensure proper care.
Locate and follow the care label
The care label is usually located on the interior portion of the garment. It will indicate if the garment is machine-washable or if it should only be hand washed or dry cleaned. Drying suggestions and water temperature parameters are sometimes included. Follow these instructions in caring for rayon or spandex garments. Be especially attentive as to what should be avoided for your garment, such as no bleach or no tumble-drying warnings.
Wash rayon with a gentle detergent
If your rayon garment allows for hand or machine washing, use only a gentle detergent. Avoid hot water and wash in lukewarm water. Use the gentle cycle when using a washing machine If the rayon fabric has not been treated with a resin finish, a chlorine bleach may be used for white rayon garments.
Wash spandex with a general-purpose detergent
When hand or machine washing spandex, your standard detergent suffices. Use warm water. Do not used chlorine-based bleach. Oxygen bleach may be used instead.
Exercise caution when drying and ironing
Rayon garments should be allowed to drip dry. If ironing is required, a medium temperature setting should be used, and the garment should be ironed on its reverse side. It is best to iron rayon while it is still slightly damp. Spandex should be line dried. If you do tumble dry spandex, do so with a low temperature setting. Ironing spandex is not recommended.