The spelling of the word "fullen" can be explained through its pronunciation, using the International Phonetic Alphabet (IPA) transcription. The word is pronounced as /fʊlən/ with the first syllable "ful" being pronounced with the vowel sound /ʊ/ as in "book" and the second syllable "len" being pronounced with the vowel sound /ə/ as in "about". The double "l" represents the sound /l/ which is pronounced with the tongue touching the roof of the mouth. The spelling of the word is consistent with the phonetic sounds it produces.