applied to the microcapsules can vary depending on the polymer that makes up the outer wall of the fibre or the microcapsules thermoplastic materials generally have a transition temperature at which the material changes from a vitreous glass state to one which is visco elastic in which the material behaves more like a viscous fluid this temperature u201c glass transition temperature u201d depends on a number of factors such as the polymer structure its molecular weight and the presence of additives such as plasticizers fibres can also be bicomponent with a softer outer wall and the core which would be a polymer of a higher melting temperature than the outside wall and above the processing temperature used for the fusion of the walls of the microcapsules with the outer wall of the fibres an example of bicomponent fibres is those used in non woven webs of fibres bound together by a process called u201c thermobonding u201d another example are thermoplastic continuous filaments used in u201c spun bonded u201d non wovens the textile substrate fibrous assembly made up of fibres and microcapsules connected together only by the points of contact of their walls does not need a binder to bind microcapsules and fibres this has several advantages relating to materials on which binders are present namely that binders are thermally conductive and lower the thermal resistivity of the fibrous assembly whereas if more air is trapped between the fibres like in the case of microcapsules fused to the fibres the resistivity of the fibrous assembly remains much the same as without microcapsules the binders used to fix the fibres in non woven webs have a higher thermal conductivity than.