Plus sofas and benches, design Yrj? Wiherheimo & Pekka Kojo. Plus is a sofa and bench system for public spaces:1-seater, 2-seater, 3-seater, 4-seater sofas. The wooden sofa back is in natural colour or stained, laminate is also available. Plus sofas are completed by square or rectangular upholstered benches. The base is made of 40x40 tubular powderpainted or chromed steel