The number of cash ISA products on the market has increased from 301 to 437 since the introduction of the personal savings allowance in 2016/17.
The personal savings allowance enables basic-rate taxpayers to receive up to £1,000 a year in tax-free savings income.
This allowance is halved to £500 for higher-rate taxpayers in the UK, while it is withdrawn for additional-rate taxpayers.
Individuals can save up to £20,000 a year into ISAs, with cash ISAs and stocks and shares ISAs among the most popular options.
Research from data provider Moneyfacts showed a 45% rise in demand for cash ISA products since April 2016, despite low interest rates offering subdued returns.
The comparison site suggested more savers are looking to cash ISAs to protect their savings for future years, fearing the allowance may be withdrawn.
Demand for fixed-rate cash ISAs surged to 23% in March 2019, while interest in variable-rate cash ISAs reached 16%.
Darren Cook, finance expert at Moneyfacts, said:
"Consumer interest in cash ISAs has increased during the latest ISA season.
"This year's [£20,000] ISA allowance will benefit from future tax relief, when interest may be much higher and the personal savings allowance may be no more.
"With the current economic outlook remaining unpredictable, savers continue to seek future security for their savings."
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