Gold leaf is readily available very thin, it can be well under 1μm. The lead sheet or foil I'm familiar with is much thicker since common uses require its density (counterweighting as you mentioned), its radiation shielding properties, and/or its easy formability by hand while holding its shape afterwards.
a_wild_redditor t1_j2eojab wrote
Reply to comment by enderjaca in How did Rutherford arrive at gold foil as the best choice for his particle experiments? by Poltibolsa
Gold leaf is readily available very thin, it can be well under 1μm. The lead sheet or foil I'm familiar with is much thicker since common uses require its density (counterweighting as you mentioned), its radiation shielding properties, and/or its easy formability by hand while holding its shape afterwards.