We report on a low-cost, environmentally friendly and wearable thermal flow sensor for non-invasive monitoring of human respiration. The sensor can be manufactured in-house using pencil graphite as a sensing hot film and biodegradable printing paper as a substrate, without using any toxic solvents or cleanroom facilities. The hot film flow sensor offers excellent characteristics such as high sensitivity, high signal-to-noise response to airflow and outstanding long-term stability. We further demonstrate a patch-type wearable sensor for monitoring human respiration. The results indicate that the sensor may be utilized to medically monitor sleep quality and other personal health concerns.