ASX exchange-traded funds (ETFs) are an increasingly popular investment choice, especially among younger investors.

In its May update on ASX ETFs, Betashares said there are now 425 ETFs trading on the ASX and CBOE exchanges.

The ETF provider said May was the eighth consecutive month in which people invested more than $3 billion into ASX ETFs.

In terms of funds under management, the ASX ETF industry is at a record high of $273.7 billion as of 31 May.

Here are two exchange-traded funds with buy ratings from experts.

Experts say buy!

Betashares Global Uranium ETF (ASX: URNM)

This ETF seeks to mirror the performance of the Indxx North Shore Uranium Mining Index before fees.

Michael Gable of Fairmont Equities has a buy rating on the Betashares Global Uranium ETF.

Earlier this month, Gable told The Bull:

URNM provides exposure to a portfolio of mining, exploration and development companies in the global uranium industry.

I'm positive about the outlook for uranium miners due to increasing demand for uranium expected to exceed supply during the next few years.

Gable pointed out that the ETF "broke out of a corrective decline on strong volumes" in late April/early May, as the following chart shows.

He commented: "… I expect the stock to move higher from here."

The ASX ETF has done exactly that, possibly sooner than Gable or the rest of us expected.

ASX uranium shares enjoyed a very strong last week on the back of an investment fund's plans to buy $200 million in physical uranium.

Boss Energy Ltd (ASX: BOE) shares rose by 20%, Deep Yellow Ltd (ASX: DYL) rocketed 30%, and Paladin Energy Ltd (ASX: PDN) lifted 17%.

The ASX URNM rose by 8.35% over the same period.

Yesterday, the ETF closed at $8.82, up 0.23% for the day and up 7.16% over the past 12 months.

Betashares S&P/ASX Australian Technology ETF (ASX: ATEC)

This ETF seeks to track the S&P/ASX All Technology Index before fees.

Commenting on The Bull this week, Andrew Wielandt of DP Wealth Advisory said the ETF gives investors exposure to about 40 shares.

These include the biggest stocks in the Australian tech sector, such as WiseTech Global Ltd (ASX: WTC) and Xero Ltd (ASX: XRO).

The ETF is also invested in companies from other market sectors that use a lot of technology in their businesses.

Examples include ASX 200 healthcare share, Pro Medicus Ltd (ASX: PME), and communication share, REA Group Ltd (ASX: REA).

The beauty of this ASX ETF is its simplicity and diversification, as Wielandt explains:

Rather than trying to pick the best Australian technology company, this ETF enables investors to have more diversified exposure to a growing industry sector. 

The ASX ATEC closed at $31.28 yesterday, up 1.53% for the day and up 29.90% over the past year.

Research from another ETF provider, Vanguard, shows ETFs are more resilient during market volatility than their underlying shares.