Colin Goulding's actions led to the loss of 100 jobs at the Real Crisp plant in Crumlin, the Daily Mirror reported. Those affected included Goulding's parents.
Judge Philip Richards, who imposed a sentence of six years and three months, said the fire affected Goulding's community as well as his employer.
"This is far and away the most serious arson I have ever dealt with as a judge in these courts," Richards said. "This was a ridiculous thing to do."
Goulding brought a pack of cigarettes and a lighter into the plant in 2012, violating company rules, and then hid in a storeroom for a cigarette break. The fire in a factory full of flammable material spread quickly.