Use 'spongy' when the softness enables soaking up liquid, similar to kitchen sponges. Her new bath mat felt comfortably spongy under her feet.
Pro Tip 2/3
Positive Connotation
'Spongy' can suggest a pleasing, soft quality in foods like cakes or bread. The fresh muffins were so spongy and light.
Pro Tip 3/3
Soft and Absorbent
Objects described as 'spongy' shouldn't resist pressure and should compress easily. The sponge cake springs back when you press it because it's spongy.