Nestlé is launching a 165-calorie chocolate bar aimed at women in its biggest-ever confectionery investment.

The launch of Kit Kat Senses on 10 March will be backed with a £9m ad spend for 2008. It is Nestlé's single-biggest spend, and as important as its launch of KitKat Chunky 13 years ago, said brand manager Brett Stephenson.

The line, two years in development, is made up of five pieces containing wafer, hazelnut praline centres and Kit Kat's traditional moulded chocolate. It is intended to bring more women into the snacking chocolate category and to Kit Kat, which overindexes with male consumers (53%). Senses is being aimed at women aged over 20 looking for an indulgent treat during their evening "me time", he added.

Although Senses has more calories and fat per 100g than the core Kit Kat, it comes in below the levels of its "indulgent" competitive set, Mars Delight and Kinder Bueno. "Senses is much more permissible than the other two, which are each more than 200 calories," said Stephenson.

The TV campaign will break in April, supported by outdoor, women's press, online activity and extensive sampling. "It's exactly the right time of year for people who are conscious about calories," said Jonathan Summerley, senior buyer at Hancocks Cash & Carry. "This will be a major launch for Nestlé and the category and the advertising supports that. It's got our backing."

Some 86% of people will see the TV ad this year and 70% of people are expected to see the outdoor campaign 20 times, said Stephenson.

According to Nielsen, the Kit Kat brand is worth £154m as a whole, up 10% in the year to December. Its four-finger line grew 27% in the year to December and is now worth £33m. Chunky was up 5% to £34m while the two-finger line was up 6% to £80m. In comparison, Mars Delight is worth £10.5m, up 26% while Kinder Bueno's sales grew 10% to £21m.

Following the UK debut, Senses (rsp 45p) will be introduced to the rest of the European market.