While traditional voluntary benefits such as life, disability, dental and vision insurance remain popular, employees are buying more “gap insurance,” especially if they are enrolled in high-deductible health plans.

Since the Great Recession, employee interest also has been growing for voluntary products that provide legal and financial protection, experts say.

According to Towers Watson & Co.'s “2013 Voluntary Benefits and Services Survey,” the percentage of employers that expect voluntary benefits to be very important to their total rewards strategy will more than double over the next five years, jumping to 48% in 2018 from 21% this year.

Top offerings employers are considering adding over the next two years are critical illness, identity theft and financial counseling, the survey of 320 employers found.

The most prevalent voluntary benefit offerings are disability, life, vision and accident care, a Mercer L.L.C. analysis reveals.

Voluntary life insurance has been a longtime workplace offering, industry experts say.

“People understand it,” said Beth Grellner, St. Louis-based national co-chair of group voluntary benefits and services at Towers Watson. “They want to provide protection for their family if something were to happen to them.”

Dental and vision also are popular but beyond those traditional voluntary benefit offerings, “accident is becoming a front-runner,” especially among young families, Ms. Grellner said. “For $4 a week, you can have an accident plan that will reimburse you for an emergency room visit when your kids need stitches. I bought it because I have kids in sports.”

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“You'll definitely see growth in accident, hospital indemnity and critical illness,” said Brian Celiberti, executive director of Crystal & Co. in New York.

Because of the trend toward high-deductible health plans and more cost-sharing, “employers are offering something to fill that gap,” said Pat Haraden, a principal at Longfellow Benefits in Boston.

For example, “sometimes they will pay up to half of the deductible,” Mr. Haraden said, whereas indemnity products “pay a flat dollar amount based on what they had done. They may get $100 for going to the emergency room or $500 or $1,000 per day for having surgery or hospitalization.”

“There are only so many dollars available to pay for these supplemental benefits,” which is why employers focus first on health-related products, said Bruce Sletten, senior vice president and national practice leader of elective benefits at Aon Hewitt in Dallas.

That said, “many mid-market employers are building up a total rewards strategy” using voluntary benefits, Mr. Sletten said.

For example, some are “offering group auto and home, which provides discounts off the retail prices that employees may be paying when purchasing these products individually,” he said. In addition, “we're seeing a fair amount of renewed interest in group legal, pet insurance and identity theft coverage.”

Dennis Healy, vice president of group sales at ARAG Insurance Co., a Des Moines, Iowa-based provider of legal insurance, said sales of his company's products have increased significantly since the recession ended.