Production of natural fibres for cloth used in garments may not be able to keep pace with demand from a growing world population. This is true of plant fibres, from cotton for instance, and animal hairs like sheep's wool and many furs. Production of artificial fibres such as the polyesters, and fabrics such as vinyl, may be subordinated to needs for chemicals in construction and in industrial applications. In addition, world weather is showing continued instability and seasonal cycles are interrupted by cold spells, hot spells, storms and droughts. This increases the demand for clothing that normally would not often be worn in certain latitudes, for example: tropical, light weight fabrics in the northern temperate zone; and heavier garments in the southern hemisphere.