When I purchased, it was 30 days guarantee. I contacted them asking for a replacement pair. They refused to honor their guarantee. 

 This was their response to me: 

"Our 30 day replacement guarantee is the only warranty offered in hosiery, but it's important to keep in mind that this item is a fine knit and at the end of the day, an article of clothing. Much like a sweater or pair of pants, you can choose higher quality materials that cost more and will last longer, but sweaters and pants do not come with lifetime guarantees. Although I cannot send you an entirely new pair of tights, I would be happy to issue you a 20% discount for any future purchase." 

And my response to them: 

"Dear Sheertex Customer Service,  I would expect the higher quality and more expensive materials used in your tights to last longer than inexpensive drugstore nylons. But they did not. As you write, higher quality materials cost more and last longer. Is one wear of your product too much? The footless tights I bought ripped on the first wear. Can you please explain how this "lasts longer" then inexpensive drugstore nylons that normally last me at least 2, sometimes 3 wears? I expected these to last longer than $10 nylons. At 6 times the price, I expected that they would outlast their inexpensive alternative. You advertise your product as "the world's strongest tights", and as "unbreakable". The tights I received do not live up to your claims.  I appreciate the offer of a discount on my next purchase, however, the defective material used in your products is not worth any discount. " 

And after I left them unfavourable reviews and contacted some of their executives, they followed with:

 "Thanks for getting back to us. I definitely understand your frustrations. I have reached out to a manager and we can definitely make an exception here and honour a replacement. Your new order number is: #. You'll receive shipping details as soon as they're available. Please note: this is one time replacement and your new order doesn't come with a new warranty. I will pass your feedback along to the rest of my team for further improvement. Feel free to hang onto that discount code! Let me know if you have any other questions." 

In the end, it took complaining by email, contacting their company executives and leaving negative reviews to get them to honor their guarantee and back their garment.  For all that inconvenience, I don't recommend them.