For men, the footwear rules during Ihram are specific: you must wear footwear that does not cover the top of the foot and leaves the ankle bones (the two protruding bones on each side of the ankle) exposed. Simple sandals, flip-flops, or open-toed slippers are the standard choices. You cannot wear regular shoes, sneakers, boots, socks, or any footwear that covers the ankle or the top of the foot. This ruling comes directly from the Prophet's instructions about what a muhrim should not wear.
Women in Ihram have no footwear restrictions. They may wear any comfortable footwear including closed shoes, sneakers, sandals, and socks. Given the extensive walking during Hajj, women should prioritize comfort and proper support in their footwear choice.
If a man genuinely cannot find sandals (which is very rare in modern times), the Prophet (peace be upon him) gave a concession to wear shoes but with the part covering the ankles cut away. In practice, comfortable walking sandals with good grip and support are essential — pilgrims walk extensively on marble and concrete surfaces that can become extremely hot during the day and slippery when wet. Break in your sandals well before the trip to avoid blisters. Many experienced pilgrims recommend sport sandals with a back strap for stability during crowded Tawaf.