assembly may incorporate a spring 24 fig3 to maintain a force on the seal 10 however once the preload is applied and the seal member 12 has undergone cold flow the preload may relax or be removed in some applications without affecting the sealing capability of the seal 10 the ferrule s 14 and washers 20 is formed of a relatively hard material suitable for the environment such as a metal material the seal member 12 is formed of a thermoplastic material that is capable of cold flow thermoplastic materials having a tensile modulus equal to or greater than 500 000 psi at room temperature are suitable for many downhole applications similarly thermoplastic materials having a flexural modulus that is equal to or greater than 500 000 psi at room temperature are suitable for many downhole applications particular thermoplastic materials that exhibit the desired cold flow characteristics for the seal 10 of the present invention are polyetheretherketone peek polypheneline sulfide pps polyetherketone pek polyetherketoneetherketoneketone pekekk polyethylene terephthalate pet and similar materials fig5 shows a seal 10 for sealing around a control line or cable 4 the control line 4 extends through a housing 8 the seal has a thermoplastic seal member 12 inside the housing 8 the seal and seal member have tapered mating surfaces mandrel 18 threadably mates with the housing 8 when the mandrel 18 is screwed into the housing 8 the mandrel 18 applies a force to the seal member 12 causing it to deform and cold flow into the gap between the control line 4 and the housing 8 the deformed seal member 12 creates the seal between the control line 4 and the housing 8.