A form for forming concrete comprises a first sheet permitting surplus water contained in the concrete cast in the form to pass through the first sheet, but capable of blocking the passage of the concrete, a second sheet secured to the first sheet, permitting the surplus water to be absorbed into it, and a plate secured to the second sheet. The first sheet provides paths for the surplus water by the existence of the second sheet. The paths for the surplus water are ensured by a spacer provided between the first sheet and the plate in lieu of the second sheet or together with the second sheet.