In 1960, Loomis became a part of the Mattel Toys sales department. From there, he moved up to marketing popular brands such as Barbie and developed a sales and marketing strategy for the Chatty Cathy talking doll.
In 1968, Loomis began developing ways to promote the new Hot Wheels boy car line for the company. One of the marketing concepts he thought of was creating an animated series based on the property, which premiered on September 6, 1969 on ABC in the US. This was the first series to be explicitly spawned from a toyline, whereas it was usually toylines that spawned from existing series. The Federal Communications Commission declared the series wasn't entertainment, but rather a thirty-minute commercial for Hot Wheels. ABC cancelled the series in 1971, but by then Loomis was already at his next toy company, General Mills.
The Hot Wheel series is the reason why Loomis was dubbed by writer David Owen as "The Man Who Invented Saturday Morning" back in 1988.