I have three sieves at home. Two of them, in different sizes, are metal ones because I have had to discard so many melted and disfigured plastic ones in the past. The only plastic one I still possess, with its fine mesh, is used almost exclusively for sifting flour; on which subject remember always to hold the sieve up high when sifting flour for pastry and cakes, to incorporate lots of air as it falls down into the bowl.
Never get a plastic colander – you are guaranteed a disaster sooner or later when it has been left too near the heat. The small aluminium or enamel ones are sturdier and safer.