my opinion on this is simple. Kesh, kara, kirpan, kanga, kachera all symbolize something important. Understanding the concept of it is more important than worry about whether your kanga is made of beech wood or oak (hehe)...kachera is used to cover the body, because in the gurus period the bahmans dressed like gandhi..all exposed in skimpy rags (to present simplicity?)..the reason why Sri guru gobind singh ji said it was important for his sikhs to present themselves in a respectful manor, and to make sikhs realise that dressing in such way wouldnt get you to vaheguru (it was a waste of time)
Worrying about materials etc is way too superficial, remember waheguru is anything and everything, god wont judge you as a "lost-follower" if you wear boxer-shorts. There are a lot of pakandee's out there claiming you should only wear steel kara n so fourth...remember gods infinite power and presence and you will soon come to realise the "significance" of your question
hope it helped
ps. im a sikh (19 years of age) i took amrit with my father- but i was only 5. although i keep uncut hair and believe in the guru's word, everything i have learnt about sikhi has been from my beloved father, im sure there are plenty of other people who can help you.. I think the best thing to do is ask yourself the question and try to answer it using common sense rather than asking for peoples (mixed) views...after all sikhi is common sense
we are just to egoistic and arrogant to realise it
bol chuk maaf