Is the felt synthetic or does it contain wool?

Dear Amazon Customer, Thank you for your interest in our purse organizer.It's my great honor to answer you this question. The felt is synthetic it is environmental friendly materials. If you have any questions or suggestion please kindly email us. We are 100% dedicated to provide you and all Amazon customers a better product and service. Best Regards Wendy

Plan to use this for the nf mm; will the large size create a boxy outline on the exterior? or is this insert "slouchy"?

Dear Amazon Cutsomer, ZTUJO bag organizer in Large size fits LV Neverfull MM very well, it will give the bag a very natural shape, and won't make it boxy. Actually there are a lot of pictures about large size organier fitting neverfull MM that our buyers uploaded, please kindly check them from our reviews.

What size would fit a birkin 35?

Dear Hannah C., We have designed a purse organizer specially for Hermes Birkin 35, please kindly click this link to place your order: https://www.amazon.com/Insert-Purse-Organizer-Bottom-Reddish/dp/B07DKDWW1Q/ref=cm_cr_arp_d_product_top?ie=UTF8 If you have any question please feel free to contact us. Best Regards, Wendy

difference betweeen slender and regular?

Dear Amzon Customer， We design Slender Large and Slender Medium based on the service of most tote bags.it more slim to fit Thin width style of purse They can give your tote bags very natural shape. Could you please kindly advise us the measurements of your bag, so that we can recommend you the suitable size? I'm looking forward to your reply. Best Regards， Wendy