Is nylon sheathing for DIY cables just window dressing?

Understood, thank you for your response. The  Mogami W3104 -12AWG 4 Conductor Speaker Cable material is solid rubber with plastic sheathing underneath separating the 4 rubber coated conductor wires, so I thought I would jut shrink wrap tube the four two conductor wires into two and shrink wrap the banana plug to the wires to keep air out. This speaker cable seems to be really good quality at roughly $6 per foot. I think leaving the nylon sheathing would save me another $100 or so, given I need a 25' length from stereo to speakers. 

No, you don't need the fancy nylon braided sleeving, they are just cable dress up. A lot of high-end cable manufacturers use them to disguise the cable used underneath or to protect their method of construction and the material used, this is especially true when a cable is advertised as being hand-built or hand-made. The heat shrink used does provide strain relief where the connectors are terminated to the cable.

Most of my DIY cables use tinned copper braid wrap for shielding and damping.  The tinned coatings rub off on your hands unless covered by Tekflex plastic braid.  Tekflex also looks nice and is relatively cheap from MacMaster Carr on-line.  Not much money in the scheme of things. 

Thanks for everyone's responses -  The Mogami W3104 -12AWG 4 Conductor Speaker Cable is not cheap at $4-6 per linear foot, but I compared them to my Cullen cable cross over series and these are as good, with a little more tightness in the bass. And as god as the Cullen cables are, they run about $30 per linear foot. BUT, for those of you looking to use standard banana plugs (like SIlverbacks) be careful as this wire is so thick, that twisting the 4 leads into 2 will barely go into standard banana plugs - you have to use the kind with the screws that go outside of the cable housing. I should know, I had to grind down the screws on the silverback banana plugs - was a pain in the a_ _ but it worked. Overall, very impressed with the sound of these cables. 

Most of my DIY cables use tinned copper braid wrap for shielding and damping. The tinned coatings rub off on your hands unless covered by Tekflex plastic braid. 

@dgarretson The OP was asking about speaker cables, do you shield those too? :)

Best,
E