Here's why:
* The "a" in "rayon" has the same sound as the "a" in "ray" or "say." This is a long "a" sound.
* Short vowel sounds are typically associated with a single vowel letter in a word and often have a shorter, sharper sound. For example, the "a" in "cat" has a short vowel sound.
So, the "a" in "rayon" is a long vowel.