Source Tube Insulator – Bicycle Tube Insulator, Black

Not sure if it makes a different. Best bet is to stuff the end down your top, then your body heat keeps the mouthpiece defrosted.

I own one for few years now and it still working perfectly.The end has a special pocket for a hand wormer that is designed to maintain a worm temperature for the valve in cold environment or a cool pack for hot weather. The hole tube cover it is made of foam that it supposed to maintain a temperature constant of the hole tube from the backpack all the way to the end.It has a zip of a decent quality and has a system to attach it to the shoulder strap of the rucksack as well.It looks very robust and never had problems with it.I did cut the plastic binner due to the reason that I needed closer to my mouth so I had to attach it on a different system. It works without but also the original system is fine just a matter of choice. If you spent 15£ on a silicone tube you must look after it so this protection it is a must buy.In the summer it is efficient as well as it will keep the liquid reasonably at constant temp. ( 2l of H2O will only be undrinkable after more than 4 hrs. at +40C temperature) so it is decent considering that it is exposed to lot of weather abuse when hiking. In the winter will probably freeze at -20C after couple of hours if the drinking frequency is too demanding. Sometimes for extra peace of mind you can blow the liquid back into the bladder and that will save time but for the hygiene reason the valve should be protected for the dust and considering that the germs like an humid environment and humans have a lot of germs inside mouth will make sense to maintain the valve sterile. I'm looking to buy another one for my tactical backpack soon it arrives and I decide what hydration system I will fit on it. Hope the seller will not put the price up after this review....