The glass is excellent; thick, durable, and beautifully dark violet that will protect your products. Read any review of Infinity Jars glass and you'll find the same thing, and these are no exception.The screw top lids are hard plastic with a foam insert. The threads are large and easy to get started so even if the jar gets messy it can be easily sealed. The foam insert looks like cheap paper at first glance, but it's proven to be water resistant and tolerates sanitizing with isopropyl alcohol so there's really nothing I can complain about. The lids can also be replaced separately for $2 (as of this writing) so the glass can remain a great investment for years and years even if the lids wear out eventually, but so far they've been durable and even scratch resistant.The only downside to these jars is that once you see them you'll want more. Expensive and valuable (or simply labor intensive) products deserve a good container, and the extra wide mouth on this one ensures you can reach every last bit of it with ease and waste none - and lose none to spoilage from sun exposure.