impermeable (adj.)

• close
• close-knit
• closed
• compact
• compressed
• concentrated
• concrete
• congested
• consolidated
• crowded
• dense
• firm
• gluey
• hard
• heavy
• hermetic
• impassable
• impenetrable
• impervious
• jam-packed
• jammed
• massive
• nonporous
• packed
• sealed
• serried
• solid
• substantial
• thick
• thickset
• unpassable
• viscid
• viscous