To compensate for his body's inability to handle One For All at its full strength, Izuku developed a way to use 20% (previously 5% which was then improved to 8%) of his Quirk's power continuously. This way, he can avoid injuring himself and disregard the need to turn his power on and off by keeping it flowing through his body. According to Izuku, this technique gives him greater maneuverability, as well as slightly enhanced strength and speed.
His enhanced mobility allows him to scale buildings with ease, clear large jumps, as well as navigate quickly through cluttered areas. He was able to find Stain and Tenya in time using this technique to run through Hosu City. His mobility even allowed him to outpace Hanta Sero during a race, someone whose Quirk also provides great mobility.
When Izuku activates Full Cowl, red vein like lines course throughout his body that coincide with the energy flowing through him. When fully active, his body and eyes start to glow with a green, electric aura.
Due to the fact that the power is spread through his body evenly rather than concentrated on a single point, the overall effects are much weaker, leaving him with only slightly superhuman traits rather than the explosive power offered by 100%.
One For All: Full Cowl - Shoot Style (ワンフォーオール フルカウル シュートスタイル Wan Fō Ōru Furu Kauru Shūto Sutairu?): While using One For All: Full Cowl, Izuku uses a fighting style that focuses more on kicking. Izuku concentrates One for All: Full Cowl's effects in his torso and legs rather than his arms, enabling him to use their naturally greater power to improve his striking strength and mobility by kicking his opponents, granting him more power and stability and allowing him to step away from the shackles of having to imitate All Might.
One For All: Full Cowl - 100% (ワン・フォー・オール フルカウル 100%パーセント Wan Fō Ōru Furu Kauru 100 Pāsento?): Izuku activates One For All to its fullest extent throughout in Full Cowl, granting him a tremendous boost in speed and strength that allowed him to easily overwhelm the likes of Overhaul. This was first used against Overhaul to protect Eri. Using this power in combination with Eri’s quirk makes yellow fire-like trails come out of his eyes. The power increase also brightens the color of his hair to a light green. Since Eri has the ability to rewind the state of a person's body, any damage done to Izuku's body by using One For All at 100% would continually be undone by Eri's Quirk.